Pygerduty

Fixed
* Fixes for Python 3.7+ compatability.
* Fixed tests for Python 3.

Changed
* Consolidated exception types to ease error handling between modules.

Fixed
* Better handling for`oncalls.list()` optional fields.

Fixed
* Better handling for`oncalls.list()` optional fields.

Fixed
* `Services.enable()/Services.disable()` fixed.

Added
* `oncalls` is a new endpoint for querying current oncalls.
* `extensions` collection added for querying extensions.

Fixed
* `incidents/{id}/snooze` was not deprecated and requires old logic from `_do_action`. Fixed.
* `trigger_summary_data` attribute was removed from incident response, removed `has_subject` function which referenced this.

Added
* `incidents/reassign` is a new endpoint, added logic for this.
* Tests for the new incidents behavior.
* LogEntries default to adding include[]=channels for list and show to get "custom details".

Fixed
- Bug with Incident.ack/resolve. This should now work.

Changed
- Renamed requester_id to requester to make it more clear you pass an e-mail now instead of user id on various Incident methods.