re-organized, commented, and messed up the RRT stuff

* Im in the process of generalizing RRTTree so that it can be used
* with other planners besides the current implementation (rather
* than just dealing with 2d points, it can handle anything
* representing state)

* Im also trying to organize things and document them better so its
* not quite as confusing to trace this code and figure out what it
* does.