Mushroom-rl

- Improved documentation;
- Added MORE algorithm;
- Added Quantile Regression DQN algorithm;
- Added wrappers for Minigrid, Habitat, iGibson (thanks to sparisi);
- Added AirHockey environments (still experimental, these environments will probably change in the future);
- Upgraded to new OpenAI gym version;
- Bug fixes in NoysiDQN, LSPI;
- Fixed ClippedGaussianPolicy, now works as expected;
- improved DMControl environment, added pixel support and arm environments e.g., 'manipulator' (thanks to jdsalmonson).

- Agent and Environment interfaces are now in core.py module.
- Added an easy interface for environment registration: environment can be created using the environment name;
- Updated Doc;
- New tutorials added;
- Improved CONTRIBUTING.md file;
- Added ConstrainedREPS;
- Bug fixed in GPOMDP;
- Improved logging of loss in regressor fit function;
- General cleanup of environment constructors;
- Improved Pybullet environment;
- Improved Voronoi tiles;
- Predict params added in DQN and Actor-Critic algorithms;
- Added support to Logger in DQN.

- Replay memory can return truncated n-step return;
- Rainbow and NoisyDQN algorithms added;
- Improved PyBullet environment;
- Added clipped Gaussian policy;
- Prediction parameters added in policy and approximator.

- Added MushroomRL logger;
- Support for wrapper args in gym environment;
- Fixes in tiles;
- Dueling DQN added;
- MDPInfo and spaces are now serializable;
- Optimizers are now serializable;
- DoubleFQI and BoostedFQI split into separate modules;
- Minor bug fixes.

- Fixes in tiles;
- Maxmin DQN and Maxmin Q-Learning added;
- Minor fixes in SAC;
- Added optimizer to policy gradient algorithms;
- Code quality improvements;
- Minor bug fixes.

- Added QLambda algorithm (thanks to nikosNalmpantis);
- Improved regressor support for Torch tensors;
- Added frames module;
- Fixed observation shape in Atari environment.