Add FlxGameJolt to flixel-addons.api package

Firstly, this is my first pull request, so if this is all messed up let me know and I'll fix it.

This pull request adds FlxGameJolt, which allows easy access to the GameJolt API, which allows for username verification, trophies, remote stored data, high score tables, and more.

I started working from an AS3 version which is mentioned in the file, however, nearly all of the code was re-written to be more efficient and to update to the latest version of the API.

FlxGameJolt is compatible with both desktop and Flash targets. If the Flash file is embedded on GameJolt's site, or if the desktop version is run from GameJolt's in-browser Quick Play feature, user name and token will be retrieved automatically.  However, you can, of course, request the user enter their info and pass that to init.  In any case, I've tried to make verifying the user credentials as painless as possible.

I tested this via Quick Play on Windows and via GameJolt-hosted Flash, and I was able to init and unlock trophies in both cases.  I believe all other classes will work, but I will test them as I enable more features in my game.

Please let me know if you need any further information. Thank you!