Add comments, make comparison less strict

Using `assertIsInstance` should allow the intent of the test to be validated
without worrying about implementation issues like "does the mock library swap
out objects under the hood?"
Merge pull request #1538 from Ichimonji10/fix-test

Add comments, make comparison less strict
Added new `subscriptions` path for Organization.

Added a new `subscriptiond` path for `entities.Organization` to
facilitate tests that need to fetch what subscriptions are available to
a given organization. Also added tests.

Finally, I updated docstrings replacing ``:return:`` entries with the
correct value of ``:returns:`` and disabled some pylint directives.