Adapted to OpenFL

Previous implementation caused "Document is missing element map" error after switching from haxe 2 + nme to haxe 3 + openfl.
Adapted to html5 target.

Previous implementation caused error while using compressed tmx maps with html5/js target. Added conditionals to prevent that behaviour (you can only use uncompressed maps with html5/js).
Merge pull request #4 from rabus/master

Solved "Document is missing element map" error and fixed html5 target issue.
Updated to haxelib json