Improve support for human readable IRIs

[jesper-friis]

In ontologies like EMMO, that uses numerical IDs, we want to refer to the concepts with human readable CURIEs consisting of a prefix and a label. For example, it should be possible to refer to the IRI https://w3id.org/emmo#EMMO_eb77076b_a104_42ac_a065_798b2d2809ad as "emmo:Atom".

Transformations in both directions should be possible.

This can be split into several subtasks:

• Namespace objects include all information (except namespace prefix) needed for these transformations. Add a method for converting a full IRI to a short human readable prefixed IRI.

  Implemented in PR: Added reverse mapping to Namespace objects using the __call__() method. #483

• Add an option to Triplestore.prefix_iri() to return human readable prefixed IRIs. Should be implemented in tripper.utils.prefix_iri(). This would require that the prefixes argument has Namespace objects as values.

• Add an option to Triplestore.expand_iri() to accept a human readable prefixed IRI as input. Should be implemented in tripper.utils.expand_iri(). This would require that the prefixes argument has Namespace objects as values.

• Make it possible to register namespaces that uses numerical IDs. This register should be checked when parsing prefixes (e.g. from a json-ld context, a keywords file, a dict, etc...). Add an utility function that takes a dict with prefix-namespace string pairs as input and return a dict mapping prefixes to Namespace objects as output. Namespace objects for numerical IDs should be created with the triplestore, label_annotations and check arguments set (the values should be fetch from the register). Ensure that this utility function is called whenever prefix-definitions are parsed.

  For efficiency, avoid duplicating Namespace objects that are created with the triplestore argument. This can be achieved with a cache mapping namespace IRIs to weakref's to created Namespace objects.

• Add option to enable support for human IRIs to all code that parses IRIs and propagate it to prefix_iri()/expand_iri(). Also ensure that prefixes are specified with namespace objects.