Modules separation

[Guigui220D]

Breaking changes

Modules (window, system, graphics, audio) are now separated. You can still use them as one this way :

const sf = struct {
    pub usingnamespace @import("sfml");
    pub usingnamespace graphics;
    pub usingnamespace window;
    pub usingnamespace system;
    pub usingnamespace audio;
};

Functions that create an object are now called create instead of init, as the csfml does, and their destructor destroy. Object created with init don't need to be destroyed.