Implement a simple binary search tree map for use in chapter 4
Expand implementations of BinarySearchTreeMap and LinkedList
Implement a simple directed graph for chapter 4. Bonus HashMap
that I was going to use in Graph, but decided not to later
Workaround for issue with RVM gemset not being detected automatically
Shrink some of the responsibilities from Graph.
Create a simple BinaryTree for use in chapter 4, not a 'real' data
structure per se, but simplifies testing certain problems in the chapter
Minor bugfix in hanoi problem in chapter 3
Remove unnecessary matchers from Guardfile
Complete exercises for chapter four