Fix haxelib package

[NQNStudios]

Closed #1.

I reorganized the files and modified haxelib.json so haxelib for Haxe 4 can locate and import the library. To test it, with haxe 4 installed:

$ git clone https://github.com/NQNStudios/hxprng.git
$ haxelib dev hxprng hxprng
$ haxelib install ihx
$ haxelib run ihx
>> addlib hxprng
>> new hxprng.PCG32().random(6)