Features:

- Replacing C++ with Rust (#424)
- Create an Index abstract base class (#556)

Improvements:

- improve error handling etc. in `sourmash lca index`. (#798)
- Move similarity with abundance computation into Rust (#808)

Bugs:

- fix mem leak in get_mins (#807)
- Fix LCA search error if query has abundance (#804)

Build, CI and docs:

- Set up MSRV, minimum supported rust version (#806)
- update docs and add recommonmark as a test dependency (#805)
- Release process updates and sourmash 3.0 release notes (#776)