Compress macros.c by representing macro directives with a single byte.
We can do this because we only use the ASCII character range inside
the standard macro files.
Note: we could save significant additional space by not having a
pointer array, and instead relying on the fact that we sweep
sequentially through the output array.
Introduce new preprocessor directives %depend and %pathsearch, and
make incbin a standard macro using these filenames. This lets us
remove the code that makes incbin search the path.
