Added GBRAM class
Added get8()
Added set8()
Added test for persistence of memory
Added Cartridge class
Added mode switching
Added protection against mode switching ROM
Added banking
Added banking for only MBC1 ROMs
Fixed exception string
Added to mode set test
Added get8()
Moved global constants outside class
Updated to use global constants defined in cart module
Implemented banking
Added spacing between top-level declarations
Added spacing between top-level declarations
Put class docstring on single line
Added EchoMem class
Added mirroring writes to echo space to RAM space