0.23.0

This release contains many bug fixes and a few small changes.

Breaking changes:

• Standardized render metadata variables ahead of render breaking change @trigaten
• Removed deprecated monitor wrapper and associated dead code @gianlucadecola
• Unused striker and thrower MuJoCo envs moved to https://github.com/RushivArora/Gym-Mujoco-Archive @RushivArora

Many minor bug fixes (@vwxyzjn , @RedTachyon , @rusu24edward , @Markus28 , @dsctt , @andrewtanJS , @tristandeleu , @duburcqa)