Small preparation before doing the actual rendering
* Read CHR in PPU
* Fix typo in PPU variable (_currentScaline -> _currentScanline)
* Actually set and clear VBlank flag like it should
* Add PPUIO interface to output pixel and to call custom code on vblank
* Update _currentPpuAddress across the frame
* Add NMI support in CPU
* Add test vlagg_vbl_clear_time but it doesn't pass for now
* Delete test in TestRunner to fix memory corruption problems
* Add basic code in main project to execute and display pixels
* Fetch and render background nametable (still work to do)
* When ROM has no CHR data, assume CHR RAM (display sprite_ram correctly)
* Emulate poorly even/odd frame in PPU
* Scale image in sukiNES (help seeing PPU bugs much easier)
* When rendering, consider palette with multiple of 4 to be at 0. Fix sky in SMB titlescreen.