Tmuxp

- 377: Include examples in source distribution package

- Loosen libtmux version constraint to >0.8 and <0.9 (libtmux 0.8.2
released today)
- 484 CHANGES converted to plain reStructuredText
- 491 `tmuxp freeze` will now infer active session with freezing
- 490 Fix XDG's `$XDG_CONFIG_HOME` behavior
- 483, 482, 480 Doc fixes
- 487 Simplifying handling of configs with no panes (Fixes
470)

- Add tests/\*.sh scripts to MANIFEST.in to include them in Pypi package.
- Include twine to dev packages on requirements and Pipfile files.

- Support Click 7.0
- Remove unused `__future__` imports
- 471 Update libtmux 0.8.0 -> 0.8.1
- 404 from anddam, support XDG base directory
- Sort imports
- Add configuration and make command for isort.
- Add sphinxcontrib-napoleon.
- Assure _requirements/dev.txt_ dependencies are in _Pipfile_
- Update sphinx, releases to latest version
- Sync _requirements/_.txt* dependencies with *Pipfile\*.
- Update docstring style to use numpy-style documentation.
This enhances readability and plays nicely with sphinx documentation.
- Documentation overhaul.

- Areas like {meth}`tmuxp.cli.load_workspace` are now documented verbosely.
This is so contributors helping on the project can more quickly gain
situational awareness in this tricky area of code.

- 431 Include tests in source distribution

- Loosen click restraint to <7