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/stdio/ftello.c

@@ -19,6 +19,7 @@
 #include "libc/calls/calls.h"
 #include "libc/errno.h"
 #include "libc/runtime/runtime.h"
+#include "libc/stdio/internal.h"
 #include "libc/stdio/stdio.h"
 #include "libc/sysv/consts/o.h"
 
@@ -29,18 +30,10 @@
  * @returns current byte offset from beginning, or -1 w/ errno
  */
 int64_t ftello(FILE *f) {
-  ssize_t rc;
   int64_t pos;
   uint32_t skew;
   if (f->fd != -1) {
-    if (f->beg && !f->end && (f->iomode & O_ACCMODE) != O_RDONLY) {
-      if ((rc = write(f->fd, f->buf, f->beg)) == -1) {
-        f->state = errno;
-        return -1;
-      }
-      if (rc != f->beg) abort();
-      f->beg = 0;
-    }
+    if (__fflush_impl(f) == -1) return -1;
     if ((pos = lseek(f->fd, 0, SEEK_CUR)) != -1) {
       if (f->beg < f->end) pos -= f->end - f->beg;
       return pos;