Make redbean StoreAsset() work better

- Better UBSAN error messages
- POSIX Advisory Locks polyfills
- Move redbean manual to /.help.txt
- System call memory safety in ASAN mode
- Character classification now does UNICODE

libc/runtime/msync.c

@@ -29,6 +29,7 @@
  * Without this, there's no guarantee memory is written back to disk. In
  * practice, what that means is just Windows NT.
  *
+ * @param addr needs to be 4096-byte page aligned
  * @param flags needs MS_ASYNC or MS_SYNC and can have MS_INVALIDATE
  * @return 0 on success or -1 w/ errno
  */