Therapist

- Revamped parser for Git status which fixes some edge case issues in
old parser.

- Fixes an issue with dependencies during setup

- Drops support for Python 3.5.
- Added support for Python 3.9.

- Residual support for Python 2 removed and added official support for
Python 3.8.
- Add `working_dir` configuration option for actions.
- Add `files_root` configuration option for actions.

- Fixes an issue where deleted files were passed to actions when the
`use-tracked-files` flag was used with the CLI.

- **Therapist no longer requires Git.**
- To maintain backwards compatibility Therapist will behave as it
previously did if the folder with the `.therapist.yml` file is the
root of a Git repo.
- A new `--disable-git` flag can be used to disable git-aware behavior
when using Therapist in a Git repo.
- A new `--enable-git` flag can be used to enable git-aware behavior.
- **Dropped support for Python 2.7 and 3.4.**
- The hook is now versioned and Therapist will complain about outdated
hooks.