rgblink: Don't allocate unnecessary buffer. Delete unused flag.
rgbasm: Don't allocate an unnecessary buffer.
rgbasm: Fix TOCTOU and reduce buffering.
Unclutter Makefile: use $Q instead of ${Q}.
Wrap Makefile to 80 characters.
Improve POSIX compliance in the Makefile.

Set .POSIX and don't use the += operator.
rgbasm: Avoid unnecessary filename copying.
Remove dead stores.
Now that we replace missing libc functions, switch back to err().
Remove rgblib.

I have never used it and it's probably been broken for years.
Update license.
Fix MinGW target.
Revert 97d431d1f4ad404e282e3781bd195be3f053734d; it breaks things.