Pullbug

- Fixes a bug where the "no pull requests" message wouldn't be used properly when draft pull requests were present but not requested as the check for pull requests happened before the filtering occured

- Fixes a bug where if both pull request and issue flags were used at the same time that pull request data would bleed into the issue messages due to reassignment of variables (variables have since been distinguished from one another)
- Bumps dev deps

- Fix the index error on retrieving requested reviewers

- Added the `author` to the messages
- Switched from `assignees` to `requested reviewers` for the `waiting on` portion of the message
- Added `base_url` paremeter to specify an enterprise GitHub instance if necessary
- Reworked the `github_token` logic to allow for better unauthenticated usage when no GitHub token is passed
- Removed support to send messages to `Rocket.Chat`
- Renamed all occurances of `GithubBug` to `Pullbug` as Gitlab was removed previously and the distinction between platforms was no longer needed. Also renamed the `github_bug` module to `bug` and made various functions used only for the tool private. Also corrects the `Messages` class name to the singular `Message`

- Moved `typed_extensions` to the list of requirements from dev requirements since we import the package in code, fixes `module not found` error

- `github_owner` is now required, was previously optional by mistake
- `github_context` now has a default of `users` restoring previously changed default behavior
- Fixes a bug where iterating over issues may have not worked due to a syntax error
- Adds `mypy` type checking
- Fixes some typing errors around default values when no parameter is passed (changes strings from `None` to an empty string to better represent the type across the whole app.)