Accelerated upscaling/filtering

[mrzzzrm]

Currently mooBoy uses a software-renderer to scale up the gameboy-framebuffer to screen resolution - this is very compatible yet slow. Where possible OpenGL should probably be used to achieve better performance and filter-enhancements.

This conflicts with the current usage of SDL_ttf. Solution: http://www.gamedev.net/topic/284259-for-reference-using-sdl_ttf-with-opengl/