Add vecenv wrappers for obs_norm to support running mujoco experiment…

… with envpool (thu-ml#628)

- add VectorEnvWrapper and VectorEnvNormObs
- obs_rms store in policy save/load
- align mujoco scripts with atari: obs_norm, envpool, wandb and README

rename save_fn to save_best_fn to avoid ambiguity (thu-ml#575)

This PR also introduces `tianshou.utils.deprecation` for a unified deprecation wrapper.

Add VizDoom PPO example and results (thu-ml#533)

* update vizdoom ppo example

* update README with results

fix conda support and keep API compatibility (thu-ml#536)

* loose constrains

* fix nni issue (thu-ml#478)

* fix coverage

Fix critic network for Discrete CRR (thu-ml#485)

- Fixes an inconsistency in the implementation of Discrete CRR. Now it uses `Critic` class for its critic, following conventions in other actor-critic policies;
- Updates several offline policies to use `ActorCritic` class for its optimizer to eliminate randomness caused by parameter sharing between actor and critic;
- Add `writer.flush()` in TensorboardLogger to ensure real-time result;
- Enable `test_collector=None` in 3 trainers to turn off testing during training;
- Updates the Atari offline results in README.md;
- Moves Atari offline RL examples to `examples/offline`; tests to `test/offline` per review comments.

bump to 0.4.4

bump to v0.4.3 (thu-ml#432)

* add makefile
* bump version
* add isort and yapf
* update contributing.md
* update PR template
* spelling check

add vizdoom example, bump version to 0.4.2 (thu-ml#384)

Fix SAC loss explode (thu-ml#333)

* change SAC action_bound_method to "clip" (tanh is hardcoded in forward)

* docstring update

* modelbase -> modelbased

Merge pull request thu-ml#302 from thu-ml/dev

v0.4.0