v2.0.0 release

• v2.0.0:
  • fix small bugs
  • adds tutorial notebooks
  • Bump ml-agents from 0.7 to 0.15 which:
    • allows multiple parallel environments for training
    • adds Soft actor critic (SAC) trainer
    • has a new kind of actions/observations loop (on demand decisions)
    • removes brains and some protobufs
    • adds side-channels to replace some protobufs
    • refactoring of the codebase
  • GoodGoalMulti are now yellow with the same texture (light emitting) as GoodGoal and BadGoal
  • The whole project including the Unity source is now available on our ml-agents fork