Opacus

Bug fixes
* Hidden states of RNN is passed to device (314)
* Validate and fix trainable modules only (316)
Miscellaneous
* Minor corrections and typo fixes in links, documentation, and tutorials.

* This release packs in lot of new features and bug fixes, and most importantly, also brings forth new APIs that are simpler, more modular, and easily extensible.
* We have bumped up the major version number from 0 to 1 and have introduced breaking changes. However, the major version bump also indicates a step-function upgrade in the capabilities.
* See [Release notes](https://github.com/pytorch/opacus/releases/tag/v1.0.0] and [Migration Guide](https://github.com/pytorch/opacus/blob/main/Migration_Guide.md) for more details about the changes.
* PR 273 contains the pointers to all the commits and PRs that went into this release.

New Features
* DDP support for faster distributed training (196)
* Support of GRU and RNN; refactored LSTM implementation (222)
* PyTorch Lightning Demo (244)
Bug fixes
* Improve nn.Linear grad sampler memory consumption (192)
* Update Opacus to stop using deprecated torch.set_deterministic (197)
* Fix optimizer.step after engine.detach()
* Test fixes
Miscellaneous
* Better validation error reporting (199)
* grad sampler type checking (241)

New features
* Major refactoring - per-sample gradient computation is separated into its own module - GradSampleModule (175)
* Improved RDP to (eps, delta)-DP conversion (162)
* Multi-GPU support (166)
Bug fixes
* Handle empty batches in Poisson sampling (164)
* Fixed memory leak from no_grad execution (180)

New features
* PackedSequence support for DPLSTM (150) (thanks touqir14 !)
Miscellaneous
* Pytest moved to dev installation (144)

This version introduces a **mildly-breaking change**: the privacy engine will now support sampling with variable batch size, just like in the Abadi et al. paper. To accommodate this feature, we have made `batch_size` a kwarg (no longer positional). We are also enforcing that all kwargs must not be specified positionally. If you had code that passed kwargs positionally, you will find an error (which will be very simple to fix).
New features
* Enforce kwargs to Privacy Engine (136).
* Fix batch construction and privacy engine (128). (thanks ConstanceBeguier!)
* Compute required sigma to reach (epsilon, delta) budget (126)
* Friendly user message for unused parameters (118).
* Print helpful message when models are not in train mode (113)
Bug fixes
* Now the Opacus package has a `__version__` attribute.
* Fix immer security issue, fix website errors
* Updated setup.py version requirements to support 3.6.8 for Windows (108) (thanks madhavajay!)
Miscellaneous
* Rewrote the grad_sample tests to use Hypothesis (125). (thanks touqir14!)