Tmuxp

- libtmux: Update to 0.10.1+ to include `Window.select_window()` fix

https://github.com/tmux-python/libtmux/pull/271

- libtmux: Update to 0.10.x

- 474 Re-release with `python setup.py sdist bdist_wheel` to
fix missing test files

- 681 Bump version to make homebrew release easier

- 681 tmuxp is now available on homebrew! Thank you jvcarli!

- 662 CI: Only update docs when changed
- 666 CI: Move test plugin packages from pyproject.toml to
pytest fixtures. Fixes 658
- 661

- Bump minimum version 3.5 -> 3.6
- Drop python 2.7 support
- Modernize syntax (remove `__future__` and modesets)
- Update black to 21.6b0