Refactored into separate findPath and walk functions

* Updated docs
* Fixed bug where bot likes to jump down steep hills
further updates to vogonistic's API ideas

 * findPathSync returns an object instead of calling a callback
 * "cannotFind" event arg is a path instead of a point
 * update to node-astar 0.1.0
 * you can know the difference between a timeout and a legitimately
   impossible path