Added Doxygen script to generate HTML documentation to /Doc/Doxygen/
Documented Sprite
Wrote documentation for Sprite
Added some more documentation to Sprite. Also, from now on rendering will always be referred to as drawing.
Documented Shader and OpenGLWindow
Cleaned up and improved various documentation
Documented Image
Added Doxygen style sheets from SFML which look quite a lot nicer
Removed the SFML Doxygen style sheet because I think it's dumb now.