MAINT: refactor of 4DD improvements

This improves on the enhancement to Py-ART 4DD wrapper which allows for
dealiasing using previously unfolded radar volumes.  This makes it possible
to dealiasing using either an unfolded volume and/or sounding data.

In addition the follow minor fixes were complete:

* Unit test for this new functionality were added.
* Python and Cython files we corrected to follow the PEP8 style guide.
* The plot_dealias.py example was updated to reflect the new syntax.