v2.0.0

The key feature of version 2 is a complete overhaul of the software design of the procedural API (i.e. Tianshou's core implementation), in which

• we establish a clear separation between learning algorithms and policies (via the separate abstractions Algorithm and Policy).
• we provide more well-defined, more usable interfaces with extensive documentation of all algorithm and trainer parameters, renaming some parameters to make their names more consistent and intuitive.
• the class hierarchy is fully revised, establishing a clear separation between on-policy, off-policy and offline algorithms
  at the type level and ensuring that all inheritance relationships are meaningful.

This release is brought to you by Applied AI Institute gGmbH.

Developers:

• Dr. Dominik Jain (@opcode81)
• Michael Panchenko (@MischaPanch)

For details, please refer to the change log.