Skrl

Added
- `MultiCategoricalMixin` to operate `MultiDiscrete` action spaces

Changed (breaking changes)
- Rename the `ManualTrainer` to `StepTrainer`
- Output training/evaluation progress messages to system's stdout
- Get single observation/action spaces for vectorized environments
- Update Isaac Orbit environment wrapper

Transition from pre-release versions (`1.0.0-rc.1` and`1.0.0-rc.2`) to a stable version.

This release also announces the publication of the **skrl** paper in the Journal of
Machine Learning Research (JMLR): https://www.jmlr.org/papers/v24/23-0112.html

Summary of the most relevant features:
- JAX support
- New documentation theme and structure
- Multi-agent Reinforcement Learning (MARL)

Added
- Get truncation from `time_outs` info in Isaac Gym, Isaac Orbit and Omniverse Isaac Gym environments
- Time-limit (truncation) bootstrapping in on-policy actor-critic agents
- Model instantiators `initial_log_std` parameter to set the log standard deviation's initial value

Changed (breaking changes)
- Structure environment loaders and wrappers file hierarchy coherently.
Import statements now follow the next convention:
- Wrappers (e.g.):
- `from skrl.envs.wrappers.torch import wrap_env`
- `from skrl.envs.wrappers.jax import wrap_env`
- Loaders (e.g.):
- `from skrl.envs.loaders.torch import load_omniverse_isaacgym_env`
- `from skrl.envs.loaders.jax import load_omniverse_isaacgym_env`

Changed
- Drop support for PyTorch versions prior to 1.9 (the previous supported version was 1.8)

Added
- JAX support (with Flax and Optax)
- RPO agent
- IPPO and MAPPO multi-agent
- Multi-agent base class
- Bi-DexHands environment loader
- Wrapper for Bi-DexHands environments
- Wrapper for PettingZoo environments
- Parameters `num_envs`, `headless` and `cli_args` for configuring Isaac Gym, Isaac Orbit
and Omniverse Isaac Gym environments when they are loaded

Changed
- Migrate to `pyproject.toml` Python package development
- Define ML framework dependencies as optional dependencies in the library installer
- Move agent implementations with recurrent models to a separate file
- Allow closing the environment at the end of execution instead of after training/evaluation
- Documentation theme from *sphinx_rtd_theme* to *furo*
- Update documentation structure and examples

Fixed
- Compatibility for Isaac Sim or OmniIsaacGymEnvs (2022.2.0 or earlier)
- Disable PyTorch gradient computation during the environment stepping
- Get categorical models' entropy
- Typo in `KLAdaptiveLR` learning rate scheduler
(Keep the old name for compatibility with the examples of previous versions.
The old name will be removed in future releases)

Changed
- Update loader and utils for OmniIsaacGymEnvs 2022.2.1.0
- Update Omniverse Isaac Gym real-world examples

Fixed
- TensorBoard writer instantiation when `write_interval` is zero