Fasteners

- Add `.acquire_read_lock`, `.release_read_lock`, `.acquire_write_lock`, and
`.release_write_lock` methods to the inter thread `ReaderWriterLock` as was
promised in the README.
- Remove support for python 3.7 and pypy 3.7. It should still work, but is no
longer tested.
- Add support for pypy 3.10 and python 3.11

- Reshuffle the process lock code and properly document it.
- Revamp the docs and switch from sphinx to mkdocs
- Remove difficult to use tread lock features from docs
- Bring back support for eventlet `spawn_n`
- Remove support for python3.6. It should still work, but is no longer tested.

- Allow writer to become a reader in thread ReaderWriter lock

- Remove unnecessary setuptools pin

- Switch to the modern python package build infrastructure

- Remove support for python 3.5 and earlier, including 2.7
- Add support for python 3.9 and 3.10
- Fix a conflict with django lock
- Add `__version__` and `__all__` attributes
- Fix a failure to parse README as utf-8
- Move from nosetest to pytest and cleanup testing infrastructure