Support for gdxAI behavior tree file format

[asciiiii]

It would be nice to have support for gdxAI behavior tree file format.

Example:
https://github.com/libgdx/gdx-ai/blob/master/tests/data/dog.tree

[BlueBoxWare]

Hi,

Sounds like a good idea, I'm going to look into that. Though it might take a while.

[BlueBoxWare]

I have added syntax highlighting for tree files. I will probably add additional functionality (formatting, completion, etc.) later.