althonos/pronto: 2.1.0

Added

• Synonym.xrefs now has a setter. (#70)
• pickle support for Ontology. (#66)
• RdfXmlParser support for owl:inverseOf and rdfs:subPropertyOf. ### Changed
• Synonym.xrefs now returns a mutable set that can be used to add Xref to the synonym directly. ### Fixed
• SynonymType.type setter does not consider all synonym types as undeclared anymore. (#71)
• RdfXmlParser crashing on synonym types definition without a label like in Uberon. (#67)
• FastoboSerializer crashing when encountering a relationship with at least one replaced_by clause.