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
`grid_shape` generalized to handle non-distributed dims.

Removes `distdims` and `ndistdim` attributes of LocalArray.

Testsuite updated and passing.
Cleans up paralleltest_localarray.py.
More refactorings relating to grid_shape.
Use `next()` from six.py
Make Python 3 happy.
Merge branch 'master' into feature/generalize-cart-comm
Move BaseLocalArray into localarray.py.
Move utility functions from base to localarray.
Remove base.py.
Rearrange imports.
Move arecompatible function (within file).
Merge BaseLocalArray into LocalArray.