Add /statusz page to redbean plus other enhancements

redbean improvements:

- Explicitly disable corking
- Simulate Python regex API for Lua
- Send warmup requests in main process on startup
- Add Class-A granular IPv4 network classification
- Add /statusz page so you can monitor your redbean's health
- Fix regressions on OpenBSD/NetBSD caused by recent changes
- Plug Authorization header into Lua GetUser and GetPass APIs
- Recognize X-Forwarded-{For,Host} from local reverse proxies
- Add many additional functions to redbean Lua server page API
- Report resource usage of child processes on `/` listing page
- Introduce `-a` flag for logging child process resource usage
- Introduce `-t MILLIS` flag and `ProgramTimeout(ms)` init API
- Introduce `-H "Header: value"` flag and `ProgramHeader(k,v)` API

Cosmopolitan Libc improvements:

- Make strerror() simpler
- Make inet_pton() not depend on sscanf()
- Fix OpenExecutable() which broke .data section earlier
- Fix stdio in cases where it overflows kernel tty buffer
- Fix bugs in crash reporting w/o .com.dbg binary present
- Add polyfills for SO_LINGER, SO_RCVTIMEO, and SO_SNDTIMEO
- Polyfill TCP_CORK on BSD and XNU using TCP_NOPUSH magnums

New netcat clone in examples/nc.c:

While testing some of the failure conditions for redbean, I noticed that
BusyBox's `nc` command is pretty busted, if you use it as an interactive
tool, rather than having it be part of a pipeline. Unfortunately this'll
only work on UNIX since Windows doesn't let us poll on stdio and sockets
at the same time because I don't think they want tools like this running
on their platform. So if you want forbidden fruit, it's here so enjoy it

libc/sock/setsockopt-nt.c

@@ -0,0 +1,60 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2021 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/calls/struct/timeval.h"
+#include "libc/macros.internal.h"
+#include "libc/sock/internal.h"
+#include "libc/sysv/consts/so.h"
+#include "libc/sysv/errfuns.h"
+
+struct linger_nt {   /* Linux+XNU+BSD ABI */
+  uint16_t l_onoff;  /* on/off */
+  uint16_t l_linger; /* seconds */
+};
+
+textwindows int sys_setsockopt_nt(struct Fd *fd, int level, int optname,
+                                  const void *optval, uint32_t optlen) {
+  struct timeval *tv;
+  struct linger *linger;
+  union {
+    uint32_t millis;
+    struct linger_nt linger;
+  } nt;
+
+  if (optname == SO_LINGER && optval && optlen == sizeof(struct linger)) {
+    linger = optval;
+    nt.linger.l_onoff = linger->l_onoff;
+    nt.linger.l_linger = MIN(0xFFFF, MAX(0, linger->l_linger));
+    optval = &nt.linger;
+    optlen = sizeof(nt.linger);
+  }
+
+  if ((optname == SO_RCVTIMEO || optname == SO_SNDTIMEO) && optval &&
+      optlen == sizeof(struct timeval)) {
+    tv = optval;
+    nt.millis = MIN(0xFFFFFFFF, MAX(0, tv->tv_sec * 1000 + tv->tv_usec / 1000));
+    optval = &nt.millis;
+    optlen = sizeof(nt.millis);
+  }
+
+  if (__sys_setsockopt_nt(fd->handle, level, optname, optval, optlen) != -1) {
+    return 0;
+  } else {
+    return __winsockerr();
+  }
+}