Add Bitfield class to replace the non-portable C bitfields in code: StatusRegister and Bits8
Improve debugging: pressing any key while stepping is disabled will enable stepping again
Fix Push16 and Pop16 resulting in stack overflow
Move components out of main into new Nes class to centralize cross-component communication (e.g. post memory read/write operations). Main loop now alternates between Cpu and Ppu updates. Implement more PPU logic, including VRAM addressing logic ($2006/$2007).