Merge branch 'feature/generalize-from_distarray' into feature/add-flat-file-io
Add basic flat-file IO and tests.
Move the details of file writing to `format.py`.
Fill in save and load implementations not using pickle.

Much of this is copied from or adapted from Numpy code.
Add a blank line.
Add and tweak some docstrings.
Remove unused imports.
Add a couple of comments about copied functions.
Add a module docstring describing the .dap format.
Edit a docstring.

Pluralize!
Add missing `comm` argument to LocalArray constructor.

Segfaults otherwise...
Refactor test_umath...

to make a client and context per-testclass rather than at the module level.
Merge branch 'feature/generalize-from_distarray' into feature/add-flat-file-io
Change flat-file extension to `.dnpy`.
Merge branch 'master' into feature/add-flat-file-io

Conflicts:
	distarray/client.py
	distarray/tests/test_umath.py