Fix up for PEP8
Add per_page param to user_issues

- Convert old test to new tests
Fix reference to iter_user_repos
Try to set auth to None on MockedSession
Add a has_auth predicate to GitHubSession
Interim mocking solution

Mock doesn't pick up attributes defined during `__init__` so it doesn't have
`headers` or `auth`. `mock.create_autospec` does not let you set these up
either so you need to work around that. :headdesk:
Much better solution to testing protected methods
Update subscriptions

- Split into subscriptions_for and subscriptions
Update all_gists

- Split into gists and public_gists
Fix up subscriptions tests