Affiliations not captured from crossref data

[seasidesparrow]

Describe the bug
For at least some crossref records, the affiliation information for each author is returned in a structure tagged as <affiliations><institution><institution_name>. (See e.g. 10.1364/AO.505607). Currently, the crossref parser is looking for the tag <affiliation> (not affiliations) and extracting the contents with .get_text(). This misses the structure above entirely.

To Reproduce
Steps to reproduce the behavior: harvest the crossref xml from their api, and parse with adsingestp.parsers.crossref. Authors 1 and 5 will have ORCIDs, but there will not be any additional affiliation information.

Additional context
Add any other context about the problem here.

[seasidesparrow]

The crossref parser is actually parsing crossref xml data that has passed through the Habanero Content Negotiation method, and so it needs to be able to read data in the UNIXREF-XML query return format, documented here: https://www.crossref.org/schema/unixref1.1.xsd.