IPFS support in default document loader

[F-Node-Karlsruhe]

We are currently looking into using IPFS as a context storage as it increases availability and conveniently takes care of versioning out of the box ("naming this with hashes"). We are using the ipfs://CONTEXT_HASH schema to reference the context. Addtionally, IPFS already provides both caching and integrity checks (versioning + trust in context).

The resolution of IPFS documents is currently implemented in the overwriting document loader like so

Is this something you would like to add in the future? If so i would make a PR regarding this topic.

The ipfs:// schema could be added here in the default document resolver
https://github.com/digitalbazaar/jsonld.js/blob/main/lib/documentLoaders/node.js#L59

[F-Node-Karlsruhe]

Evolved into PR #513