Support for IRI references (#59)

[jakubklimek]

This would add support for IRI references in $id, $ref and $dynamicRef as per #59

[Relequestual]

Please DO NOT MERGE this yet. 2020-12 meta-schema needs to be published.

[Relequestual]

Additionally, the specification documents would need updating, either first (in a separate PR), or at the same time.

[karenetheridge]

$vocabulary and $schema use uri - should this be changed to iri?

[jakubklimek]

@karenetheridge yes, we want the references to be IRIs as well so that they are also human readable

[handrews]

@jakubklimek I'm going to convert this to a draft as there seems to still be discussion in the issue.

[jakubklimek]

@Relequestual @handrews I have pushed commits changing URIs to IRIs in the spec as well where necessary. I left references to RFC 3986 (URIs) wherever resolving base URIs is mentioned, as this is also applicable to IRIs and RFC 3987 actually refers to RFC 3986 in this manner.

I would therefore like to resume discussions about merging this.

[jdesrosiers]

Thanks for doing this work! I noticed that there seem to be a few unrelated changes that got mixed in to this PR as well. It looks like it's coming from a merge from master. Could you have a look and clean that up?