4.3 Schema Update

[tmorrell]

Add ROR as funderIdentifierType and small json validation fix

[tmorrell]

Just realized that affiliation identifiers were also missed in the 4.3 schema. I just added them to this PR.

[tmorrell]

This PR makes the assumption that there can be multiple affiliation identifiers, which might not be the case in 4.3. Waiting on DataCite for clarification.

[tmorrell]

I've updated the schema to match DataCite naming and support only one identifier per #78. Travis is failing because of an unrelated Ruby dependency. This is ready for review @mfenner

[satra]

any updates on merge of these schema changes or what is holding this back? we are building some converters from our data model to post to datacite, and would very much appreciate if we could validate with a schema locally before upload. it seems that the schema in this PR aligns with the datacite API more than the one in the main branch of this repo.

[KellyStathis]

@tmorrell Thanks very much for these corrections to schema 4.3!

I've also added a note to the directory https://github.com/datacite/schema/tree/master/source/json with a bit of context for the JSON schema. Although an official, DataCite-supported JSON schema is in our backlog, the JSON schemas for 4.2 and 4.3 here are primarily community contributions. Huge thanks to @tmorrell, @lnielsen, @mark-saeon, and others for your work on this.