Esmre

* Fixes `pip install esmre` failure due to incompatibility with Cython 3 (thanks Rictus)
* Removes dependency on unmaintained module nose. This change also removes support for deprecated `python setup.py test`. Use `python -m unittest` instead.

esmre has been used in production for about 15 years. I'm confident it is now ready to leave beta testing.

This version carries only minor changes:

* Update package metadata.
* Apply consistent code formatting with [black](https://github.com/psf/black).
* Fix a couple of [flake8](https://github.com/pycqa/flake8) warnings.

Release 0.5.2 belatedly adds support for Python 3.

* replace the handwritten C extension with a Cython-generated module
* apply updates from underlying ESM implementation
* fix a syntax error
* convert unicode strings to utf8 bytes where required
* apply minor modernization