Unflatten

No substantive code changes from 0.1.1.

Features

- Added type annotations.

Testing

- Test under python 3.10, 3.11, and 3.12.

- Fix tox config to cope with the fact that recent tox/virtualenv does
not support EOLed versions of python.

Nits

- Fix backslashes in docstrings

Packaging

- PEP517-ize the packaging
- Use `setuptools-scm` to maintain version numbers

Testing

- Test under Python 3.7, 3.8, 3.9 and PyPy 3.7. Drop testing for Python 3.4 & 3.5.
- Pin pip version for pypy2 (see [pip 8653][])
- Clean up and modernize the tox `lint` and `coverage` environments

[pip 8653]: https://github.com/pypa/pip/issues/8653

No code changes.

This package is now deemed "production ready" (though your mileage may vary.)

Initial release.