Pycldf

- Added option to `downloadmedia` subcommand to customize file naming.

- Fixed bug whereby foreign keys for the ParameterNetwork component were not added correctly because
of an incorrect specification in terms.rdf. (See also https://github.com/cldf/cldf/issues/161)

- Fixed bug whereby `dict` returned by `orm.Language.as_geojson_feature` could not be serialized
by `json.dumps`.
- Fixed bug whereby SQLite conversion would fail when the name of a renamed column clashed with an
existing column name in the table.
- Emit warning when encountering invalid main part for mediaType property.

Fixed bug whereby component names where the CSV filenames contain underscores were not translated
appropriately when creating the SQLite db. (Note that this fix is required for the ParameterNetwork
component in CLDF 1.3.)

Support for CLDF 1.3.

- Support typed values, specified via `columnSpec` in `ParameterTable` in `orm` module.
- Better datatype descriptions when rendering metadata as markdown.
- Run tests on python 3.12