Includes proper string representation.

Boot ROM improvements

See merge request !47

Improved build system for the boot ROMs.
Better comments in the ROM code.

Created the `vebose` mode for diagnostics.

Allows usage of pytest for testing python code.

Custom Boot ROM support

Closes #34

See merge request !46

CGB is now going to boot using Boytacean ROM by default.
Allows better image and open source only boot.

Making it possible to indirectly access the registers via constants.

Adds OBP0_ADDR and OBP1_ADDR to the list of registers.