Ignore rom files
Removed working memory pointer

After reading futher documentation on the gameboy color's memory system
it turns out that my originl plan to just have a single contiguous block
of memory isn't effective.

Instead I'll store the cartridge header and then bank pointers with some
proper MMU behaviour.
Add header and bank fields to gameboy structure
Make gameboy_close free memory banks
Differentate between ROM and RAM banks

This patch differentiates the ROM and RAM banks, so they are treated
separately to avoid confusion (and bugs).
Add len paramter to gameboy_load stub
Add stub definition for gameboy_step declaration.
Accept rom file path from command line