Added an XHR helper for easy cross-browser get requests.
Added and implemented a preloader so only the first level has to be initially loaded. See #32.
Moved transitioner back to ig.game.
Fixed an incorrect typeof check where instanceof should be used.
Added a config to enable/disable the preloader.
Merge pull request #57 from bdaenen/E-32-defer_level_loading

E 32 defer level loading