0.15 Release

[davidhewitt]

Quite a number of improvements and fixes have now accumulated on main since the 0.14 releases. In addition, Python 3.10 has now been released, so I think a PyO3 release soon with "official support" for Python 3.10 would be welcomed by the community.

The 0.15 milestone still has quite a few open pieces in it, however none of them are strictly required to be completed for 0.15 to be released so I may rearrange these into a future milestone. In particular, for various reasons I'm not as far along with #1884 as I'd hoped, however I'll try to make some more progress on it soon if I can.

There are, however, a few things which I'm aware of which I think do need completing before we put out 0.15:

• I'd like to add some mention of Migrating #[pyproto] to #[pymethods] #1884 in the guide so that users can start giving us feedback on the __dunder__ methods in #[pymethods], even if we say it's experimental for now.
• The anyhow integration in Add anyhow-integration feature which implements From<anyhow::Error> for PyErr #1822 should be merged so that it can be released alongside the eyre integration from Implement eyre feature #1893.