Pycircleci

* Refactor string formatting to use f-strings

* Add endpoint to get user repos

* Add support for Circle-Token header based auth

* Update deprecated Retry option

* Add more insights endpoints (API v2)
* Add more pipeline endpoints (API v2)
* Add more user endpoints (API v2)
* Add more workflow endpoints (API v2)
* Add schedule endpoints (API v2)

* Fix get_contexts()
* Add endpoints for context environment variables (API v2)