Introduce RDFParser and RDFWriter implementation for Newline Delimited JSON-LD format

[desislava-hristova-ontotext]

A "Newline Delimited JSON" exists, see NDJSON website and specification. Similar to it, a multiline JSON-LD is used in the community, i.e in Springer Nature SciGraph dataset.

Implement an RDFParser and RDFWriter that reads/writes such a format and thereby formalize the format:

• Each line is a JSON-LD object
• Empty lines allowed (same as Newline Delimited JSON) as it is more flexible
• MIME type: application/x-ld+ndjson derived from the existing MIME type for JSON-LD application/ld+json and the MIME type of Newline Delimited JSON application/x-ndjson
• File extension: .ndjsonld derived from the file extension for JSON-LD .jsonld and the file extension for Newline delimited JSON .ndjson.