get_ref_info returns a character string or a vector with information from one of the
metadata fields in a Data Store reference's associated xml file.
Arguments
- holding_id
The six-seven digit reference / holding ID number unique to the data store record.
- field
is one of the following: "Title" returns the title of the data store reference as a string value; "Abstract" returns the abstract as a string value; "Citation" returns the citation as a string value, and "Keywords" returns a vector containing all keywords as character values.