* feat: add support for xonsh
* xonsh: add STARSHIP_SESSION_KEY
* xonsh: implement STARSHIP_SESSION_KEY in xonsh
* docs: mention tcsh, elvish, and nu in more places
* xonsh: change STARSHIP_SESSION_KEY implementation
See https://github.com/starship/starship/pull/2807#discussion_r667064149
* xonsh: fix jobs implementation
* xonsh: do not silently discard stderr from starship
