Major changes
- Add package tests and Travis CI support. ([56](https://github.com/eonu/sequentia/pull/56))
- Remove Python v3.8+ support. ([56](https://github.com/eonu/sequentia/pull/56))
- Rename `normalize` preprocessing method to `center`, since it just centers an observation sequence. ([62](https://github.com/eonu/sequentia/pull/62))
- Add `standardize` preprocessing method for standardizing (standard scaling) an observation sequence. ([63](https://github.com/eonu/sequentia/pull/63))
- Add `trim_zeros` preprocessing method for removing zero-observations from an observation sequence. ([67](https://github.com/eonu/sequentia/pull/67))
Minor changes
- Add `Validator.random_state` for validating random state objects and seeds. ([56](https://github.com/eonu/sequentia/pull/56))
- Internalize `Validator` and topology (`Topology`, `ErgodicTopology`, `LeftRightTopology`) classes. ([57](https://github.com/eonu/sequentia/pull/57))
- Use proper documentation format for topology classes. ([58](https://github.com/eonu/sequentia/pull/58))