v0.21.0 Release Notes

• The old Atari entry point that was broken with the last release and the upgrade to ALE-Py is fixed (@JesseFarebro)
• Atari environments now give much clearer error messages and warnings (@JesseFarebro)
• A new plugin system to enable an easier inclusion of third party environments has been added (@JesseFarebro)
• Atari environments now use the new plugin system to prevent clobbered names and other issues (@JesseFarebro)
• pip install gym[atari] no longer distributes Atari ROMs that the ALE (the Atari emulator used) needs to run the various games. The easiest way to install ROMs into the ALE has been to use AutoROM. Gym now has a hook to AutoROM for easier CI automation so that using pip install gym[accept-rom-license] calls AutoROM to add ROMs to the ALE. You can install the entire suite with the shorthand gym[atari, accept-rom-license]. Note that as described in the name name, by installing gym[accept-rom-license] you are confirming that you have the relevant license to install the ROMs. (@JesseFarebro)
• An accidental breaking change when loading saved policies trained on old versions of Gym with environments using the box action space have been fixed. (@RedTachyon)
• Pendulum has had a minor fix to it's physics logic made and the version has been bumped to v1 (@RedTachyon)
• Tests have been refactored into an orderly manner (@RedTachyon)
• Dict spaces now have standard dict helper methods (@Rohan138)
• Environment properties are now forwarded to the wrapper (@tristandeleu)
• Gym now properly enforces calling reset before stepping for the first time (@ahmedo42)
• Proper piping of error messages to stderr (@XuehaiPan)
• Fix video saving issues (@zlig)

Also, Gym is compiling a list of third party environments to into the new documentation website we're working on. Please submit PRs for ones that are missing: https://github.com/openai/gym/blob/master/docs/third_party_environments.md

Full Changelog: v0.20.0...v0.21.0