Change knn_graph to return an edge list rather than an adjacency matrix. Also update syntax and options in epsilon_graph.
Add adjacency list conversion and self-edge removal utilities.
Renamed functions in pythonic style and expanded confusing abbreviations.
Substitue networkx for igraph in main tree construction method. Saved the igraph version igraph_tree.py. Still need to clean up the latter and test each for accuracy.
Clean up the igraph tree module. Still contains both adjacency list and matrix version; the matrix version can probably be deleted when I'm sure the new versions are working properly.
Remove duplicate setup lines from igraph tree.
Add kd-tree and ball tree options (from scikit-learn) to the knn-graph utility and update the epsilon graph utility.
Add unit tests for similarity graph and density estimation utilities.
Start level set tree unit tests, especially the density grid. Not ready to run, let alone merge into dev.
Add unit tests for density grid and generic tree correctness, and replaced the pandas dependency with prettytable.