Plotter should sort with default settings upon initialization
Implement ``plot_tree`` method
Added a ``plot_contour`` method
Added ``plotter()`` and ``viewer()`` methods for ``Dendrogram`` for convenience, and also speed up GUI by a factor of 2x by avoiding calling ``draw()`` twice for every slider action (the slider calls ``draw()`` by default).
Round the slice index in interactive viewer
Started writing documentation on plotting/visualizing results
Added example data file
Added pip-requirements file for readthedocs
Added examples of plotting contours
Merge pull request #33 from astrofrog/plotting-docs

Add tutorial/docs for visualization