Improve docs on behavour trees and builders #78

I just can not understand what happened while I was not paying attention to the Botcraft.
What are those trees? Why trees? Why not just handlers of packets and simple loops?
What is this hell?! (https://github.com/adepierre/Botcraft/blob/master/Examples/4_MapCreatorExample/src/main.cpp#L280)
Where is good old onTick or onPacket?
What does selector, inverter, leaf, end and sequence do? Where can I find how to make my own trees?
In my opinion such trees add unnecessary complexity to the code, build up backtraces and require much more additional calls...