[Experimental] Move the fork of HScript into Polymod

[EliteMasterEric]

Polymod was previously using a modified HScript-ex. Since that was built on top of the normal HScript package, we were using that.

Lately, the experimental branch has required using a specific fork of hscript, located at https://github.com/FunkinCrew/hscript/.

This has frustrated the process of making another stable release of the Polymod haxelib (which I haven't gotten around to doing in over a year).

Since the new HScript is required on that branch, we might as well fold it into Polymod proper. This would also make it easier to make improvements since they would only have to be made on one repo.

We could also start merging together the classes, like hscript.Interp and PolymodInterpEx, as appropriate, to simplify the codebase.