Behavior tree poolable

[mgsx-dev]

As discussed in #12, here is changes to make behavior trees poolable.

Pool strategy can be configured as follow :

• If you need to pool entire trees, you can use the PooledBehaviorTreeLibrary implementation (or one of yours). Pools are indexed by tree reference. Shouldn't be used if you modify tree after creation.
• If you need to pool individual tasks types, you have to implement pooling in your TaskCloner.
• By default, trees and tasks are not pooled at all (for compatibility).

@davebaol : there is one minor impact in wiki (call to "reset" method have to be replaced by "resetTask") but i can't PR wiki changes with github. Maybe a pool subtopic would be helpful for developers.

Please feel free to make suggestions about design/code, I'll try to fix ASAP.

[davebaol]

Sorry for being late.
I'm going to merge this PR if you fix the conflicts and update Parallel#reset in order to take into account the orchestrator

[mgsx-dev]

It should be OK now.

[davebaol]

Thanks @mgsx-dev

[davebaol]

@davebaol : there is one minor impact in wiki (call to "reset" method have to be replaced by "resetTask")

Done!
Could you please quickly document this feature?

[mgsx-dev]

Sure! I added something in the wiki : https://github.com/libgdx/gdx-ai/wiki/Behavior-Trees#pooling. Please review it, English is not my native language :-).

[davebaol]

Great work! Thanks