* feat: requires-python
refactor: updating to current proposal
fix: add tests and fix a few issues
docs: Update mostly from @joerick
docs: update README from readthedocs
* refactor: pull out config file reading
* fix: always assume highest Python patch version
* refactor: try new design
* refactor: function and bump MyPy to 0.800
* fix: tighten AST to call only, add docs
* fix: address review points from @joerick
