Reference the distributed array protocol in docs.
Correct a couple of docstrings.

One was generating a sphinx warning.
Fix API reference.
Fix another sphinx warning.
Mention optional matplotlib dependency.
Add matplotlib to travis build...

to build the api reference for plotting.py.
Replace 'pngmath' extension with 'mathjax'...

to avoid having to install LaTeX.  I don't think we're using much if any math notation anyway.

Also removed the unused `html_static_path`.
Merge branch 'master' into feature/update-docs
Fix LocalArray.copy()
Add some LocalArray.copy tests.
Add simple array value tests.
Add a simple docstring to LocalArray.copy.
Factor out an assertion method for testing.
Fix astype and add tests.
Remove a skipped test.
Partially fix LocalArray.view().

Raise NotImplemented in a case that didn't work properly.
Add some simple docstrings and a TODO comment.
Merge branch 'master' into feature/update-docs
Comment out the matplotlib pip install.
denselocalarray -> localarray in docs