Handle multiple affiliations in Zenodo for CFF 1.3.0+

[alexlancaster]

This is an incomplete draft pull request to partially implement multiple affiliations once the upstream schema change is merged in to CFF v1.3.0 in https://github.com/citation-file-format/citation-file-format/pull/523

This PR:

• is missing unit tests for the moment
• overrides the base class in cff_1_x_x/authors/zenodo to create an affiliations: key in .zenodo.json if a list is present, otherwise defaults back to the affiliation key.
• uses the ror if present, but outputs it as id for Zenodo backend.

[alexlancaster]

I'm thinking that this support should perhaps actually be in the base class ZenodoAuthor (in cff_1_x_x/authors/zenodo )? since it appears that's where new functionality goes even if it's not supported in that particular version of the schema, because the validation would catch it before it would try and use the multiple affiliation output. Is that right?