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/stubs/ld.S

@@ -44,10 +44,12 @@
 
 //	Thread local boundaries defined by linker script
 //	@see	ape/ape.lds
-	_tbss_start = 0
-	_tbss_end = 0
 	_tdata_start = 0
 	_tdata_end = 0
+	_tdata_size = 0
+	_tbss_start = 0
+	_tbss_end = 0
+	_tls_size = 0
 
 	.globl	_base
 	.globl	ape_xlm
@@ -63,10 +65,12 @@
 	.globl	_end
 	.globl	_ereal
 	.globl	_etext
-	.globl	_tbss_start
-	.globl	_tbss_end
 	.globl	_tdata_start
 	.globl	_tdata_end
+	.globl	_tdata_size
+	.globl	_tbss_start
+	.globl	_tbss_end
+	.globl	_tls_size
 	.globl	__data_start
 	.globl	__data_end
 	.globl	__bss_start
@@ -86,10 +90,12 @@
 	.weak	_end
 	.weak	_ereal
 	.weak	_etext
-	.weak	_tbss_start
-	.weak	_tbss_end
 	.weak	_tdata_start
 	.weak	_tdata_end
+	.weak	_tdata_size
+	.weak	_tbss_start
+	.weak	_tbss_end
+	.weak	_tls_size
 	.weak	__data_start
 	.weak	__data_end
 	.weak	__bss_start