Add raw memory visualization tool to redbean

This change introduces a `-W /dev/pts/1` flag to redbean. What it does
is use the mincore() system call to create a dual-screen terminal
display that lets you troubleshoot the virtual address space. This is
useful since page faults are an important thing to consider when using a
forking web server. Now we have a colorful visualization of which pages
are going to fault and which ones are resident in memory.

The memory monitor, if enabled, spawns as a thread that just outputs
ANSI codes to the second terminal in a loop. In order to make this
happen using the new clone() polyfill, stdio is now thread safe.

This change also introduces some new demo pages to redbean. It also
polishes the demos we already have, to look a bit nicer and more
presentable for the upcoming release, with better explanations too.

libc/stdio/putwchar.c

@@ -22,6 +22,6 @@
  * Writes wide character to stdout.
  * @return wc if written or -1 w/ errno
  */
-wint_t putwchar(wchar_t wc) {
-  return fputwc(wc, stdout);
+wint_t putwchar_unlocked(wchar_t wc) {
+  return fputwc_unlocked(wc, stdout);
 }