Add initial implementation of RDF Patch parser.

[recalcitrantsupplant]

Summary of changes

Introduces support for parsing RDF Patch files, aligned to the specification here: https://afs.github.io/rdf-delta/rdf-patch.html

Supports:

• Adding and Deleting triples and quads from a Dataset.
• Adding and Deleting prefixes from a Dataset.
• blank node ID preservation from input documents. That is, blank nodes are NOT document scoped when parsing patches. blank nodes can be specified either using the format:
  • _:identifier
  • <_:identifier> both will be parsed as blank nodes and their identifier from the document they are parsed from preserved.

Known limitations:

• No support yet for Patch logs (a series of Patch files)

Checklist

• [x] Checked that there aren't other open pull requests for the same change.
• [x] Checked that all tests and type checking passes.
• If the change adds new features or changes the RDFLib public API:
  • [x] ~Created an issue to discuss the change and get in-principle agreement.~ Discussed with a number of maintainers TODO:
  • [x] Considered adding an example in ./examples.
  • [x] Considered adding additional documentation.

[coveralls]

coverage: 90.617% (+0.01%) from 90.605% when pulling 72622447edf4dc6d880c3690c673e4691af96f8d on recalcitrantsupplant:david/rdf-patch-parser into cb5d05812552ec76739b518bccb9f900c9cfe8ec on RDFLib:main.

[ashleysommer]

@edmondchuc Merging is blocked on your pending review. Can you please re-review and approve to so we can merge it.