Tmuxp

- Port `tmuxp debug-info` from 643 from via v1.6.2

- 530 Plugin system

- Add plugin system for user customization of tmuxp
- Add tests for the plugin system
- Update existing tests for the plugin system
- Add the plugin interface to the tmuxp package
- Add in depth documentation for the plugin system

Thank you joseph-flinn!

- 665 Support for passing tmux config file (`-f`), thanks jfindlay! Fixes
654

- 651 Fix packaging issue with click, thanks dougharris! Fixes
649

- 647 Adding option to dump `load` output to log file, thank you
joseph-flinn!

`tmuxp load file.yaml --log-file yourfile.txt`

Adjust log levels:

`tmuxp --log-level DEBUG load file.yaml --log-file yourfile.txt`

- 643 New command `tmuxp debug-info` for creating github
issues, fixes 352. Thank you joseph-flinn!

(v1-6-1)=