Added function to unload textures. Call this in the destructor of anything that loads a texture from loadTexture.
DO NOT EVER LOAD A TEXTURE OUTSIDE OF loadTexture!
Added gfx namespace.
Added gfx::Texture class, which should abstract SDL_Texture and handle loading and managing copies of textures efficiently.
Moved state::Game from state_game.h to state.h
Added additional functionality to Rect<T>, including a constructor and helper functions.
Added gfx::Sprite class to support the gfx::Texture class. Modeled (read: copied) from SFML Sprite and Texture class. They make rendering things so much easier.