Major changes
- Rework preprocessing module (see [177](https://github.com/eonu/sequentia/pull/177)). ([#179](https://github.com/eonu/sequentia/pull/179))
- Add `Custom` transformation.
- Rename `Preprocess` to `Compose`.
- Don't validate observation sequences after each transformation in `Compose`.
- Remove progress bars and `verbose` parameter.
- Stop unnecessarily copying each observation sequence before transformations.
- Change `transform()` function on `Transform` objects to accept a single observation sequence.
- Remove `_apply()` function on `Transform` objects.
- Make `_is_fitted()` public on `Transform` objects (change to `is_fitted()`).
- Use `__str__` instead of `_describe()` for transformation descriptions.
- Remove need to send `DeepGRU` to device explicitly, so we can now do `DeepGRU(..., device=device)` instead of `DeepGRU(..., device=device).to(device)`. ([178](https://github.com/eonu/sequentia/pull/178))
- Add `dev`, `test`, `docs` and `notebooks` extras. ([174](https://github.com/eonu/sequentia/pull/174))
- Remove `Equalize` transform as it goes against the point of variable-length sequence classification. ([172](https://github.com/eonu/sequentia/pull/172))
- Change `TrimZeros` transform to `TrimConstants`, allowing any constant-valued observation to be trimmed. ([172](https://github.com/eonu/sequentia/pull/172))
- Add DeepGRU classifier implementation. ([169](https://github.com/eonu/sequentia/pull/169))
- Add `sequentia[torch]` extra for optional `torch` CPU installation. ([169](https://github.com/eonu/sequentia/pull/169))
Minor changes
- Keep batch lengths on CPU ([pytorch/pytorch43227](https://github.com/pytorch/pytorch/issues/43227)). ([#178](https://github.com/eonu/sequentia/pull/178))
- Remove `docs/requirements.txt` and specify `docs` extra in `.readthedocs.yml`. ([176](https://github.com/eonu/sequentia/pull/176))
- Move Sphinx extensions from `docs/conf.py` to `requirements.py`. ([176](https://github.com/eonu/sequentia/pull/176))
- Bump development status classifier to beta. ([175](https://github.com/eonu/sequentia/pull/175))
- Move package dependency specifications to `requirements.py`. ([174](https://github.com/eonu/sequentia/pull/174))
- Add `docs/README.md`, `notebooks/README.md` and `lib/test/README.md`. ([174](https://github.com/eonu/sequentia/pull/174))
- Update HMM classifier diagram. ([173](https://github.com/eonu/sequentia/pull/173))
- Add build status to `README.md`. ([171](https://github.com/eonu/sequentia/pull/171))
- Fix patch description in `CONTRIBUTING.md`. ([170](https://github.com/eonu/sequentia/pull/170))
- Fix wording in `README.md`. ([167](https://github.com/eonu/sequentia/pull/167), [#168](https://github.com/eonu/sequentia/pull/168))