Pronto

Added
- Explicit support for Python 3.8.
- Support for Windows-style line endings
([53](https://github.com/althonos/pronto/issues/53))

Fixed
- Handling of some clauses in `FastoboParser`.
- `OboSerializer` occasionaly missing lines between term and typedef frames.
Added
- Missing docstrings to some `Entity` properties.

Fixed
- `RdfXMLParser` crashing on entities with `rdf:label` elements
without literal content.

Fixed
- `pronto.serializers` module not being embedded in Wheel distribution.

Added
- `Entity.add_synonym` method to create a new synonym and add it to an entity.
- `roundrepr` now adds a minimal docstring to the generated `__repr__` method.
- `Ontology` caches subclassing relationships to greatly improve performance of
`Term.subclasses`.
Changed
- `Entity` subclasses now store their `id` directly to improve performance.
- `Term.subclasses` and `Term.superclasses` use `collections.deque` instead of
`queue.Queue` as a LIFO structure since thread-safety is not needed.
- `chardet` result is now used even when prediction confidence is under 100%
to detect encoding of the handle passed to `Ontology`.
Fixed
- `SynonymType` comparison implementation.
- `Synonym.type` getter crashing on `type` not being `None`.
- `RdfXMLParser` crashing on synonymtypedefs without scope specifiers.

Fixed
- Issues with typedef serialization in `FastoboSerializer`.
- `Ontology.create_term` and `Ontology.create_relationship` not raising `ValueError`
when given an identifier already in the knowledge graph.
- Signature of `BaseSerializer.dump` to remove `encoding` argument.
- Missing `__slots__` in `Entity` in non-typechecking runtime.
Changed
- Bumped `fastobo` requirement to `v0.6.0`.