Context takes a client argument, no longer takes view.

Context initializes its view attribute with all engines from the client
passed in.  Will initialize with Client() if no client argument
provided.

User can (still) select a subset of client's engines with `targets`
argument.
Removes direct_view instances from testsuite.
Clean up test_client.py's docstring.
Merge branch 'master' into bugfix/context-takes-client

Conflicts:
	distarray/tests/test_client.py
	distarray/tests/test_distributed_io.py
Merge branch 'master' into bugfix/context-takes-client

Conflicts:
	distarray/tests/test_client.py
	distarray/tests/test_distributed_io.py
Merge pull request #212 from enthought/bugfix/context-takes-client

Context takes a client argument, no longer takes view