Make repo haxelib-friendly

[AustinEast]

This PR just makes some minor changes to make hlimgui usable through haxelib. You still have to copy over the .hdll to your project's root (would be nice if haxelib could handle this, but im not sure if it can), but this is a nice start 👍

Cliff notes:

• Adds a haxelib.json so haxelib can register the library
• Moves the sample (Main.hx) to the src directory so it doesn't interfere when the root directory is scanned by haxelib

[haddock7]

Thanks @AustinEast I really appreciate your work!
Can you do add your name to the contributor list in haxelib.json?

[haddock7]

I don't think that Haxelib can handle currently this kind of library which includes native binaries. But you're right, it's a good start.

[AustinEast]

Can you do add your name to the contributor list in haxelib.json?

Done! And I might end up asking around about .hdll support with haxelibs, hopefully it'd be an easy add 👍