v2.0.0

Melting Pot Version 2.0.0 release. See Melting Pot 2.0 Tech Report for detailed information on the new substrates, bots, and scenarios.

Changed

• Removed all v1 scenarios, bots, and substrates and replaced with new versions.
• Scenarios now support heterogenous roles, which must be specified at build
  time.
• Various improvements to examples and their documentation.

Added

• New puppeteers and policies to implement new bots.
• New utils to handle sprites, colors, and maps.
• Mocks for use in testing.