Implement emulator host/renderer

[taylus]

This would be e.g. a MonoGame desktop app which hands input off to GBDotNet.Core and receives screen data to draw from GBDotNet.Core's PPU, "hosting" the emulator core that is gbdotnet. Kind of similar architecture to Bizhawk w/ its multiple emulator cores.

Try using https://github.com/taylus/monogameboy as a starting point.