Added initial NROM Mapper class
Migrated to SDL2.0

Things still need work though. Like:
* Console text entry. There's probably a more appropriate way to take textual input in SDL2.0.
* Getting a basic system loop going that involves the CPU and PPU.
* Backing commands for pausing and continuing the NES execution.
* PPU rendering to an SDL surface.
* An easy way to test PPU rendering.