Fixing Sphinx warnings and preventing more from occurring.
Merge pull request #277 from dhermes/fix-sphinx-warnings

Fixing Sphinx warnings and preventing more from occurring.
Implements group_by, projection and offset on datastore Query.

In addition, __eq__ was implemented on datastore.key.Key
to allow for easy comparison.
Remove notes about datetime.date objects and timezone matching.

Issues #278 and #279 have been filed to address.
Document regression tests, make run_regression fail if environ not set.
Adding support for queries in regression test.

This is an attempt port the gcloud-node regression tests
for queries over to gcloud-python.

This surfaced some API differences (i.e. issue #280)
and some missing features (projection, offset and group_by).

In addition, __eq__ was implemented on datastore.key.Key
to allow for easy comparison within tests.