Pronto

Added
- Deprecation warnings for the retrieval of relationships via
indexing, to be deprecated in `v3`.
Changed
- Replaced Travis-CI with GitHub Actions to handle continuous integration.
- Bumped `fastobo` dependency to `v0.10.0`.
Removed
- Retrieval of terms via their alternate IDs (introduced in `v2.3.0`,
caused multiple issues ([120](https://github.com/althonos/pronto/issues/120),
[126](https://github.com/althonos/pronto/issues/126)).

Added
- Support for path-like objects when creating an `Ontology`
([108](https://github.com/althonos/pronto/pull/108)).
Fixed
- Avoid decoding file-like objects if they are already **UTF-8**
encoded when creating an `Ontology`
([110](https://github.com/althonos/pronto/pull/110)).

Fixed
- `pronto.entity` package not being included in source distribution.

Added
- Retrieval of entities via their alternate IDs on the source `Ontology`.
- Direct edition of entity relationships via the `Relationships` view.
- `__all__` attribute to all modules of the data model.
- `RelationshipSet` container like `TermSet` with shortcut attributes and
proxying of actual `Relationship` instances.
- `Relationship.subproperties` and `Relationship.superproperties` methods
to add, remove, clear and iterate over the subproperties and superproperties
of a `Relationship` instance.
- `Ontology.synonym_types` method to count (via `SizedIterator`) and iterate
over the synonym types of an ontology and all of its imports.
- `Ontology.get_synonym_type` method to retrieve a single synonym type by ID
from an ontology or one of its imports.
Changed
- Management of sub-properties / super-properties is now consistent with
the management of subclasses / superclasses.
- `consider`, `disjoint_from`, `disjoint_over`, `equivalent_to`, `replaced_by`
`transitive_over` and `union_of` properties of `Relationship` now return
a `RelationshipSet`.
Fixed
- Outdated documentation in `Term.subclasses` describing the performances of
the previous algorithm.
- Possible `AttributeError` with the setter of the `Entity.synonyms` property.
- Issue with synonym types declared in imported ontologies not being usable
with synonyms of the actual ontology.
- Various type annotations not updated since version [v2.2.2].

Changed
- Make `Entity.annotations` return a mutable set and add a setter.
Fixed
- `Term.relationship` erroneously updating the `Ontology._lineage` cache.
- Unneeded code in `pronto.serializers._fastobo` handling `is_a` clauses.

Changed
- Replaced `frozendict` with `immutabledict` ([90](https://github.com/althonos/pronto/pull/90)).
- Bumped `fastobo` dependency to `v0.9.0` to support inline comments.
- Parsers will now process their imports in parallel using a thread pool.
Fixed
- Argument type checking in view layer is now disabled during the parsing
phase to reduce overhead.