v2022.06.0rc0

This pre-release brings a number of bug fixes and improvements, most notably a major internal refactor of the indexing functionality and the use of flox_ in groupby operations. It also stops testing support for the abandoned PyNIO.

Many thanks to the 39 contributors:

Abel Soares Siqueira, Alex Santana, Anderson Banihirwe, Benoit Bovy, Blair Bonnett, Brewster Malevich, brynjarmorka, Charles Stern, Christian Jauvin, Deepak Cherian, Emma Marshall, Fabien Maussion, Greg Behm, Guelate Seyo, Illviljan, Joe Hamman, Joseph K Aicher, Justus Magin, Kevin Paul, Louis Stenger, Mathias Hauser, Mattia Almansi, Maximilian Roos, Michael Bauer, Michael Delgado, Mick, ngam, Oleh Khoma, Oriol Abril-Pla, Philippe Blain, PLSeuJ, Sam Levang, Spencer Clark, Stan West, Thomas Nicholas, Thomas Vogt, Tom White, Xianxiang Li