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/underlong.c

@@ -0,0 +1,85 @@
+/*-*- 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/intrin/pcmpgtb.h"
+#include "libc/intrin/pmovmskb.h"
+#include "libc/mem/mem.h"
+#include "libc/str/str.h"
+#include "libc/str/thompike.h"
+#include "libc/str/tpenc.h"
+#include "net/http/escape.h"
+
+/**
+ * Canonicalizes overlong Thompson-Pike encodings.
+ *
+ * Please note that the IETF banned these numbers, so if you want to
+ * enforce their ban you can simply strcmp() the result to check for
+ * the existence of banned numbers.
+ *
+ * @param p is input value
+ * @param n if -1 implies strlen
+ * @param z if non-NULL receives output length
+ * @return allocated NUL-terminated buffer, or NULL w/ errno
+ */
+char *Underlong(const char *p, size_t n, size_t *z) {
+  uint64_t w;
+  char *r, *q;
+  size_t i, j, m;
+  wint_t x, a, b;
+  int8_t v1[16], v2[16], vz[16];
+  if (z) *z = 0;
+  if (n == -1) n = p ? strlen(p) : 0;
+  if ((q = r = malloc(n + 1))) {
+    for (i = 0; i < n;) {
+      memset(vz, 0, 16); /* 50x speedup for ASCII */
+      while (i + 16 < n) {
+        memcpy(v1, p + i, 16);
+        pcmpgtb(v2, v1, vz);
+        if (pmovmskb((void *)v2) != 0xFFFF) break;
+        memcpy(q, v1, 16);
+        q += 16;
+        i += 16;
+      }
+      x = p[i++] & 0xff;
+      if (x >= 0300) {
+        a = ThomPikeByte(x);
+        m = ThomPikeLen(x) - 1;
+        if (i + m <= n) {
+          for (j = 0;;) {
+            b = p[i + j] & 0xff;
+            if (!ThomPikeCont(b)) break;
+            a = ThomPikeMerge(a, b);
+            if (++j == m) {
+              x = a;
+              i += j;
+              break;
+            }
+          }
+        }
+      }
+      w = tpenc(x);
+      do {
+        *q++ = w;
+      } while ((w >>= 8));
+    }
+    if (z) *z = q - r;
+    *q++ = '\0';
+    if ((q = realloc(r, q - r))) r = q;
+  }
+  return r;
+}