* Pin cython to below version 3
Cython 3 includes backwards incompatible changes so it's no longer
possible to install pycapnp from source.
* Add py311 environment
I'm not sure if this is necessary, but 3.11 is out so might as well?
- Full cleanup of all the docs
- General sphinx housekeeping
- Updated all the old/bad links
- More reliable tests
- Updated Changelog
- Removed dead/deprecated code
- Added documentation generation test