Pullbug

- Use `woodchips` for logging
- Adds missing `__all__` variable for importing
- Adds Python type hinting, stronger tests
- Small bug fixes

Breaking Changes

- Completely removes `GitLab` support as I no longer use the platform and can't reliably test its functionality nor have a desire to maintain that piece. For those looking to still use Pullbug's GitLab feature, you can use any version of Pullbug prior to `v3.0.0`
- Replaces all env variables with CLI args for a more uniform experience, various shortcodes for flags were changed or removed as a part of this process (closes 24)
- Replaces the `--wip` flag with `--drafts` to use the newer GitHub draft boolean to determine if a pull request is a draft or not (closes 28)
- Now requires the `--github_context` flag for explicit logic routing
- Now requires the `--pulls` or `--issues` flag for explicit logic routing

Other Changes

- Added new `--repos` flag to filter repos you want pull requests for (closes 23)
- Added new `--issues` flag to bug GitHub for issues instead of pull requests. No includes `--pulls` flag to help differentiate (closes 19)
- Switched from raw API calls to `PyGithub` which allows us to properly handle pagination (closes 14)
- Replace all `classmethods` with instance or static methods
- Various bug fixes and code refactor

- Drops support for Python 3.6
- Swaps `mock` library for builtin `unittest.mock` library
- Formats entire project with `Black`

- Pin dependencies
- Fix typos in classmethod decorators

- Command line arguments are now validated at runtime and their defaults have been set in code (closes 22)
- If there is no assignee to a pull request, we will now populate the `waiting on` message with `NA` instead of leaving it blank
- Small code refactor and improved test coverage

- Adds Discord support. Now you can send Pullbug messages to a Discord webhook (closes 17)
- Completely rewrote the message module. Messages are now an array of messages built from PR/MR data. This allows messages to be broken up easily into batches for chat services such as Discord which may require multiple batches of messages due to character limit
- The repo name is now included in each message with a link to the repo (closes 16)
- Reworked tests to be more clean and uniform
- Various bug fixes and code refactor for better performance and maintainability