Make improvements

- Document redbean's argon2 module
- Fix regressions in cthreads library
- Make testlib work better with threads
- Give the cthreads library lots of love
- Remove some of the stdio assembly code
- Implement getloadavg() across platforms
- Code size optimizations for errnos, etc.
- Only check for signals in main thread on Windows
- Make errnos for dup2 / dup3 consistent with posix

This change also fixes a bug in the argon2 module, where the NUL
terminator was being included in the hash encoded ascii string. This
shouldn't require any database migrations to folks who found this module
and productionized it, since the argon2 library treats it as a c string.

libc/stdio/unlocked/clearerr_unlocked.S

@@ -1,30 +0,0 @@
-/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8     -*-│
-│vi: set et ft=asm ts=8 tw=8 fenc=utf-8                                     :vi│
-╞══════════════════════════════════════════════════════════════════════════════╡
-│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
-│                                                                              │
-│ Permission to use, copy, modify, and/or distribute this software for         │
-│ any purpose with or without fee is hereby granted, provided that the         │
-│ above copyright notice and this permission notice appear in all copies.      │
-│                                                                              │
-│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
-│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
-│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
-│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
-│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
-│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
-│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
-│ PERFORMANCE OF THIS SOFTWARE.                                                │
-╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/macros.internal.h"
-
-//	Clears error state on stream.
-//
-//	@param	rdi has stream pointer
-//	@see	clearerr_unlocked()
-//	@threadsafe
-clearerr:
-	mov	%rdi,%r11
-	ezlea	clearerr_unlocked,ax
-	jmp	stdio_unlock
-	.endfn	clearerr,globl

libc/stdio/unlocked/feof_unlocked.S

@@ -1,30 +0,0 @@
-/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8     -*-│
-│vi: set et ft=asm ts=8 tw=8 fenc=utf-8                                     :vi│
-╞══════════════════════════════════════════════════════════════════════════════╡
-│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
-│                                                                              │
-│ Permission to use, copy, modify, and/or distribute this software for         │
-│ any purpose with or without fee is hereby granted, provided that the         │
-│ above copyright notice and this permission notice appear in all copies.      │
-│                                                                              │
-│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
-│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
-│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
-│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
-│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
-│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
-│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
-│ PERFORMANCE OF THIS SOFTWARE.                                                │
-╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/macros.internal.h"
-
-//	Returns true if stream is in end-of-file state.
-//
-//	@param	rdi has file stream object pointer
-//	@note	EOF doesn't count
-//	@see	feof_unlocked()
-//	@threadsafe
-feof:	mov	%rdi,%r11
-	ezlea	feof_unlocked,ax
-	jmp	stdio_unlock
-	.endfn	feof,globl

libc/stdio/unlocked/ferror_unlocked.S

@@ -1,30 +0,0 @@
-/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8     -*-│
-│vi: set et ft=asm ts=8 tw=8 fenc=utf-8                                     :vi│
-╞══════════════════════════════════════════════════════════════════════════════╡
-│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
-│                                                                              │
-│ Permission to use, copy, modify, and/or distribute this software for         │
-│ any purpose with or without fee is hereby granted, provided that the         │
-│ above copyright notice and this permission notice appear in all copies.      │
-│                                                                              │
-│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
-│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
-│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
-│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
-│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
-│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
-│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
-│ PERFORMANCE OF THIS SOFTWARE.                                                │
-╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/macros.internal.h"
-
-//	Returns nonzero if stream is in error state.
-//
-//	@param	rdi has file stream object pointer
-//	@note	EOF doesn't count
-//	@see	ferror_unlocked()
-//	@threadsafe
-ferror:	mov	%rdi,%r11
-	ezlea	ferror_unlocked,ax
-	jmp	stdio_unlock
-	.endfn	ferror,globl

libc/stdio/unlocked/fgetc_unlocked.S

@@ -1,30 +0,0 @@
-/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8     -*-│
-│vi: set et ft=asm ts=8 tw=8 fenc=utf-8                                     :vi│
-╞══════════════════════════════════════════════════════════════════════════════╡
-│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
-│                                                                              │
-│ Permission to use, copy, modify, and/or distribute this software for         │
-│ any purpose with or without fee is hereby granted, provided that the         │
-│ above copyright notice and this permission notice appear in all copies.      │
-│                                                                              │
-│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
-│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
-│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
-│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
-│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
-│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
-│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
-│ PERFORMANCE OF THIS SOFTWARE.                                                │
-╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/macros.internal.h"
-
-//	Reads byte from stream.
-//
-//	@param	rdi has stream object pointer
-//	@return byte in range 0..255, or -1 w/ errno
-//	@see	fgetc_unlocked()
-//	@threadsafe
-fgetc:	mov	%rdi,%r11
-	ezlea	fgetc_unlocked,ax
-	jmp	stdio_unlock
-	.endfn	fgetc,globl

libc/stdio/unlocked/fgets_unlocked.S

@@ -1,37 +0,0 @@
-/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8     -*-│
-│vi: set et ft=asm ts=8 tw=8 fenc=utf-8                                     :vi│
-╞══════════════════════════════════════════════════════════════════════════════╡
-│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
-│                                                                              │
-│ Permission to use, copy, modify, and/or distribute this software for         │
-│ any purpose with or without fee is hereby granted, provided that the         │
-│ above copyright notice and this permission notice appear in all copies.      │
-│                                                                              │
-│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
-│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
-│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
-│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
-│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
-│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
-│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
-│ PERFORMANCE OF THIS SOFTWARE.                                                │
-╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/macros.internal.h"
-
-//	Reads line from stream.
-//
-//	This function is similar to getline() except it'll truncate
-//	lines exceeding size. The line ending marker is included
-//	and may be removed using _chomp().
-//
-//	@param	rdi is output buffer
-//	@param	rsi is size of rdi buffer
-//	@param	rdx is file stream object pointer
-//	@return	rax has rdi on success, NULL on error or
-//		NULL if EOF happens with zero chars read
-//	@see	fgets_unlocked()
-//	@threadsafe
-fgets:	mov	%rdx,%r11
-	ezlea	fgets_unlocked,ax
-	jmp	stdio_unlock
-	.endfn	fgets,globl

libc/stdio/unlocked/fgetwc_unlocked.S

@@ -1,30 +0,0 @@
-/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8     -*-│
-│vi: set et ft=asm ts=8 tw=8 fenc=utf-8                                     :vi│
-╞══════════════════════════════════════════════════════════════════════════════╡
-│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
-│                                                                              │
-│ Permission to use, copy, modify, and/or distribute this software for         │
-│ any purpose with or without fee is hereby granted, provided that the         │
-│ above copyright notice and this permission notice appear in all copies.      │
-│                                                                              │
-│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
-│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
-│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
-│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
-│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
-│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
-│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
-│ PERFORMANCE OF THIS SOFTWARE.                                                │
-╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/macros.internal.h"
-
-//	Reads UTF-8 wide character from stream.
-//
-//	@param	rdi has stream object pointer
-//	@return wide character or -1 on EOF or error
-//	@see	fgetwc_unlocked()
-//	@threadsafe
-fgetwc:	mov	%rdi,%r11
-	ezlea	fgetwc_unlocked,ax
-	jmp	stdio_unlock
-	.endfn	fgetwc,globl