Continual-inference

Added
- Support for `GroupNorm` and `InstanceNorm`

Added
- `append` function to `co.Sequential`.
- Production-ready docstrings for public functions.
- reduce_max to `Reduce`.

 Changed
- Rename `Unity` to `Identity` to follow `torch.nn`.
- Major overhaul of README, improving descriptions and adding benchmark.
- Major overhaul of docs, improving descriptions and adding benchmark.
- MHA warnings to only log once.

Removed
- Unused parameters `batch_first` and `bidirectional` for RNN, GRU, and LSTM.

Fixed
- `co.Conditional` onnx support for single-option config.

Fixed
- `co.Conditional` onnx support.

Fixed
- `co.Conv` onnx export for kernel_size=1.

Added
- Ability to access onnx from root, i.e. `co.onnx`.