go wrapper of AntTweakBar

this is just a wrapper of the AntTweakBar from Philippe Decaudin, I did not write the original library. This wrapper is used and test in working code. The ant tweak bar is included in this repository for simplicity. And yes callbacks work perfectly fine.

By the way, this works with SDL2, too.

Have fun to use this, there is no simpler UI for 3D applications.