Added hull.py (from dynamiq r199).
Corrected permissions on hull.py. (644, not 755)
Draft of hull_volume; minor additions to hull.

I'm keeping the original hull.py file separate so that I can easily sync it
between msm-tis and dynamiq. I've generated a separate hull_volume file for
the msm-tis Volume object version.
Oops; forgot to add hull_volume in previous commit.
Implemented potentially useful methods in hull.py.

* `hull_facets()`: returns vertex numbers to describe the facets on the
  hull.
* `vertex_list_to_points()`: return spatial points for a list of vertices
  (maintaining array shape)
Betters docs for hull and hull_volume.
Merge pull request #5 from dwhswenson/hull_volume_iss2

Adds hull and hull_volume.