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

net/http/isreasonablepath.c

@@ -0,0 +1,67 @@
+/*-*- 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/str/str.h"
+#include "libc/str/thompike.h"
+#include "net/http/http.h"
+
+/**
+ * Returns true if path doesn't contain "." or ".." segments.
+ *
+ * @param size if -1 implies strlen
+ * @see IsAcceptablePath()
+ */
+bool IsReasonablePath(const char *data, size_t size) {
+  const char *p, *e;
+  int x, y, z, a, b, i, n;
+  if (size == -1) size = data ? strlen(data) : 0;
+  z = '/';
+  y = '/';
+  x = '/';
+  p = data;
+  e = p + size;
+  while (p < e) {
+    x = *p++ & 0xff;
+    if (x >= 0300) {
+      a = ThomPikeByte(x);
+      n = ThomPikeLen(x) - 1;
+      if (p + n <= e) {
+        for (i = 0;;) {
+          b = p[i] & 0xff;
+          if (!ThomPikeCont(b)) break;
+          a = ThomPikeMerge(a, b);
+          if (++i == n) {
+            x = a;
+            p += i;
+            break;
+          }
+        }
+      }
+    }
+    if (x == '\\') {
+      x = '/';
+    }
+    if (z == '/' && y == '.' && x == '/') return false;
+    if (z == '/' && y == '.' && x == '.') return false;
+    z = y;
+    y = x;
+  }
+  if (y == '/' && x == '.') return false;
+  if (z == '/' && y == '.' && x == '.') return false;
+  return true;
+}