Refactoring hxMikMod for compatibility with Haxe 3.

I noticed this would no longer compile due to various changes in Haxe 3, so I made a few updates:

* Hashes changed to Maps
* refactored TrackerEventDispatcher to not extend EventDispatcher to avoid static/instance name clashes
* changed UInts to Ints (not sure if this is a good solution, but UInts and Ints can't be compared)

After these changes, I was able to compile it and play a .xm file.