Support mappings to other KOS then classifications

[nichtich]

Known classification systems can be mapped to with skos:exactMatch with MARC field 065. Looking for the right place to put exact mappings to other knowledge organization systems I found 7XX - Heading Linking Entries, e.g. 750. The particular KOS can be given in $2 as MARC code e.g. from Subject Heading and Term Source Codes.

[danmichaelo]

Support for 7XX has been added, but will have to be extended to support $1 if MARC PROPOSAL NO. 2017-08 ("Use of Subfields $0 and $1 to Capture Uniform Resource Identifiers (URIs) in the MARC 21 Formats") is accepted.