Yesgraph

- Removes the GET /followers/<type>/<identifier> endpoint
- Fixes the GET /client-key/ endpoint to work with requests version 2.8

- Adds POST /backfill/address-book endpoint for POSTing address-books without returning ranked results

- Adds POST /invite-sent (single entry) and POST /invite-accepted (single entry) deprecated endpoints back in for compatibility
- Updates tests

- Updates POST /invite-sent (single entry) to POST /invites-sent (list)
- Updates POST /invite-accepted (single entry) to POST /invites-accepted (list)
- Adds GET /followers/<type>/<identifier>
- Adds test coverage and support for Coveralls
- Adds POST /suggested-seen
- Adds filters to /address-book endpoint
- Removes GET /users
- Removes POST /facebook
- Removes GET /address-books

- Deprecate the `invitee_id` and `invitee_type` fields in the Invites API
endpoints
- Require keyword arguments for the Invites API endpoints

- Set User-Agent header