- Support for "typed values" in `StructureDataset`s
- More convenient access to targets of foreign key constraints via
`Dataset.get_foreign_key_reference`
- Existence of components/columns can now be checked with `name in Dataset`
- Added `Dataset.components` property, to allow convenient access to components
specified in a dataset.
- Enhanced and refactored documentation (see https://pycldf.readthedocs.io/en/latest/).