Issue rdflib jsonld 85 - link header support in URLInputSource

[datadavev]

Fixes specifically rdflib-jsonld-85 by adding general support for following link headers in URLInputSource.

Proposed Changes

• Added method parse_link_header
• Follow link header when media type and optionally a provided profile match
• Added test cases

[coveralls]

Coverage decreased (-0.08%) to 75.438% when pulling 95f23e5 on datadavev:issue_rdflib-jsonld_85 into 1b77d03 on RDFLib:master.

[nicholascar]

@datadavev thanks for this PR. I recall the issue you are addressing now. I'll just need to think about this for a day or two and chat with another person (see below) about this before approving. Just want to ensure the handling doesn't get in the way of other Content Negotiation stuff.

@rob-metalinkage can you take a look at this? This may solve an issue for JSON-LD but create issues for other RDF formats. We need to discuss before accepting.

[rob-metalinkage]

A quick explanation of when jsonld should be following a link header - on parsing inputs?

My only concern is that the parser should work properly if the JSON-LD uses contexts - and should support serialisation respecting use of contexts rather than brute-force turning everything into full URIs - JSON-LD should support serialisation to specific schemas with contexts.