Implemented CPU rendering for current ObjectTypes

RECT_FILLED (easy), RECT_OUTLINE (ok I need to maths), CIRCLE_FILLED (oh my god how do I maths)

Screen::RenderPixels is FITH but can see the correct(ish) output in "cpu_rendering_last_frame.bmp"

TODO:
 - Fix Screen::RenderPixels
 - Fix reading a BMP from the screen (so we can do "gpu_rendering_last_frame.bmp" as well)
 - Put Beziers in
 - Implement infinite precision document format
 - Profit