Ignore the `build` directory.
Remove unnecessary, commented code.

This change shouldn't affect anything.

Code was left behind in `bmfont.c` after the XML parser was split
off into `xmlparser.c`; this code was useless and has been removed.
Removed unused static func `BMFont_Copy8BitImage`

8-bit images aren't supported yet and it may be a while before they
are; I need to figure out how SDL deals with 8-bit images and how
SDL_Palette plays into that.

Regardless the function was not used. It didn't even have a
declaration.