Images

[Rapptz]

Find a way to wrap up SDL2_image. This allows loading of pngs, jpegs, etc.

[Rapptz]

This is mostly finished. I decided that an sdl::image should be added and differentiate it from sdl::sprite (which is part of #14). sdl::sprite would deal with SDL_RenderCopyEx while sdl::image would be SDL_RenderCopy. I am not sure if sdl::image would be like sf::Image and be essentially SDL_Surface*.

[Rapptz]

Decided on the latter. sdl::image doesn't exist. Just sdl::surface. So this issue is fixed.