This is one of the built-in variables for Make and can increase
portability on different operating systems (eg, on Windows, the
built-in $(RM) may be defined as "del" instead of "rm -f").
This eliminates another author-name directory. PLAYPAL and COLORMAP
generation are separate operations that are really only very vaguely
related to one another. Move these into separate, logically-named
directories.
As part of this we eliminate the symlinks for the PLAYPAL and various
colormap lump files, and instead copy these into the parent directory
for use by deutex. This brings further progress on #202.
