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

examples/nc.c

@@ -0,0 +1,112 @@
+#if 0
+/*─────────────────────────────────────────────────────────────────╗
+│ To the extent possible under law, Justine Tunney has waived      │
+│ all copyright and related or neighboring rights to this file,    │
+│ as it is written in the following disclaimers:                   │
+│   • http://unlicense.org/                                        │
+│   • http://creativecommons.org/publicdomain/zero/1.0/            │
+╚─────────────────────────────────────────────────────────────────*/
+#endif
+#include "libc/calls/calls.h"
+#include "libc/fmt/conv.h"
+#include "libc/log/log.h"
+#include "libc/macros.internal.h"
+#include "libc/runtime/runtime.h"
+#include "libc/sock/sock.h"
+#include "libc/str/str.h"
+#include "libc/sysv/consts/af.h"
+#include "libc/sysv/consts/ipproto.h"
+#include "libc/sysv/consts/poll.h"
+#include "libc/sysv/consts/shut.h"
+#include "libc/sysv/consts/so.h"
+#include "libc/sysv/consts/sock.h"
+#include "libc/sysv/consts/sol.h"
+
+/**
+ * @fileoverview netcat clone
+ *
+ * Implemented because BusyBox's netcat doesn't detect remote close and
+ * lingers in the CLOSE_WAIT wait possibly due to file descriptor leaks
+ *
+ * Once upon time we called this command "Telnet"
+ */
+
+int main(int argc, char *argv[]) {
+  ssize_t rc;
+  size_t i, got;
+  char buf[1500];
+  int err, toto, sock;
+  struct linger linger = {true, 1};
+  struct sockaddr_in addr = {AF_INET};
+  struct pollfd fds[2] = {{-1, POLLIN}, {-1, POLLIN}};
+
+  if (argc != 3) exit(1);
+  inet_pton(AF_INET, argv[1], &addr.sin_addr);
+  addr.sin_port = htons(atoi(argv[2]));
+
+  if ((sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) == -1) {
+    perror("socket");
+    exit(1);
+  }
+
+  if (setsockopt(sock, SOL_SOCKET, SO_LINGER, &linger, sizeof(linger)) == -1) {
+    perror("setsockopt(SO_LINGER)");
+    exit(1);
+  }
+
+  if (connect(sock, &addr, sizeof(addr)) == -1) {
+    perror("connect");
+    exit(1);
+  }
+
+  fds[0].fd = 0;
+  fds[1].fd = sock;
+  for (;;) {
+    fds[0].revents = 0;
+    fds[1].revents = 0;
+    if (poll(fds, ARRAYLEN(fds), -1) == -1) {
+      perror("poll");
+      exit(1);
+    }
+
+    if (fds[0].revents & (POLLIN | POLLERR | POLLHUP)) {
+      if ((rc = read(0, buf, 1400)) == -1) {
+        perror("read(stdin)");
+        exit(1);
+      }
+      if (!(got = rc)) {
+        shutdown(sock, SHUT_WR);
+        fds[0].fd = -1;
+      }
+      for (i = 0; i < got; i += rc) {
+        if ((rc = write(sock, buf + i, got - i)) == -1) {
+          perror("write(sock)");
+          exit(1);
+        }
+      }
+    }
+
+    if (fds[1].revents & (POLLIN | POLLERR | POLLHUP)) {
+      if ((rc = read(sock, buf, 1500)) == -1) {
+        perror("read(sock)");
+        exit(1);
+      }
+      if (!(got = rc)) {
+        break;
+      }
+      for (i = 0; i < got; i += rc) {
+        if ((rc = write(1, buf + i, got - i)) == -1) {
+          perror("write(stdout)");
+          exit(1);
+        }
+      }
+    }
+  }
+
+  if (close(sock) == -1) {
+    perror("close");
+    exit(1);
+  }
+
+  return 0;
+}