Pullbug

- Fixed bug where arguments weren't being passed properly to the `run_missing_checks` function.
- Beefed up tests to ensure args were being passed to this function

- Adding missing `main` entrypoint function that was accidentally deleted during code refactor for v2.0.0

- Replaced `logger.warning` with `logger.error` as they were used incorrectly (closes 15)

- Correcting references of "Pull Bug" to "Pullbug"

- Instead of raising an error when no pull or merge requests can be found, we return that message. This is helpful when a user wanted to use both GitHub and GitLab in a single invocation. The previous implementation would exit the script without running the other.

- Added context for GitHub, you can now get personal pull requests in addition to orgs
- Added logging both to console and to a file. Logs will rollover when their size gets too big
- Added various error handling that was missing
- Added unit tests and code coverage
- Bumped character count from 100 to 120 for descriptions on messages
- Assignees are now checked against the assignee array instead of a single assignee if there are multiple
- Bumped pagination from 20 to 100 items
- Updated documentation
- Various settings now have default values
- Introduced various new settings that can be altered
- Various bug fixes