Sentinel

First stable release.

This stabilizes all features in 0.3.0, without significant changes to the modules behaviour.

Added

- `sentinel.create()` infers name from assignment statement
- requires optional requirement: [python-varname](https://github.com/pwwang/python-varname)

I messed up the release :/

* test: deepcopy

* remove: examples.py

These old code samples make me cringe >.<


* deps: add varname as an optional dependency

* feat: infer variable name if name is not provided

* test: skip if varname is not installed

* docs: rewrite for latest version

* 0.3.0-alpha.0

Added

- calling the type() of a sentinel returns the singleton instance

Changed

- `sentinel.create()` keyword argument: `extra_methods` is now `cls_dict`

Attempting to publish to PyPI via GitHub Actions