v3.3

Summary

New metric: sea-ice metric, implementation led by @acordonez

What's Changed

• Sea ice metrics beta by @acordonez in #1024 (Contributors: @durack1 @gleckler1 @lee1043)
• update readme by @lee1043 in #1016
• Clean up that were left from testing by @lee1043 in #1017
• Add more for stats branch by @lee1043 in #1018
• update by @lee1043 in #1019
• Stats function moved to be better shared across metrics by @lee1043 in #1014
• Update version number in setup.py by @lee1043 in #1021
• environment.yml for binderhub on LLNL nimbus by @lee1043 in #1023
• Fix typo in doc by @acordonez in #1025

Full Changelog: v3.2...v3.3