#1 Change #includes of SDL headers to be more portable

[Chris Martin]

Several files include SDL headers using a syntax like:

#include <SDL/SDL.h>

The libsdl project recommends that SDL headers be included as thus:

#include "SDL.h"

This change would allow files to compile on Mac OS X using the SDL frameworks, which are deployed without the SDL subdirectory.

The files affected by this change (as of 0.1):
Window.cpp
Uzi2d.h
Texture.h
Texture.cpp
Sprite.cpp
Rect.h
Polygon.cpp
Framerate.h
Font.cpp

There are additional files affected in the "SpaceInvaders" example project:
player.h
main.cpp
game.h
alien.h