Added a method "registerArchetypeTree" to the class BehaviorTreeLibrary
to have the possibility to add archetype behavior trees programatically
instead of loading from files, as suggested in the comments at
https://github.com/libgdx/gdx-ai/issues/12
Made registerArchetypeTree public and fixed formatting
Added a test (which can be executed lazy or non lazy) based on the
existing include subtree tests.
Merge pull request #21 from tomvangreen/master

Programatically registering of btree archetypes in BehaviorTreeLibrary