[fromxml] Handle multiple value matches in templates

[proycon]

In a configuration like the following:

[[elements.annotationdata]]
set = "https://ns.huc.knaw.nl/textannodata.jsonld"
key = "recipient"
value = """{{ $./tei:teiHeader/tei:profileDesc/tei:correspDesc/tei:correspAction[@type="received"]/tei:rs[@type="person"] }}"""     skip_if_missing = true

The value template matches and returns only the first matching element (by design). We don't have a proper mechanism yet
to deal with multiple matches (in this example: multiple recipients)

[proycon]

A solution is now implemented (pending release), it would look like this in the configuration. The difference being the $$ selector instead of $, to indicate we want all matches, and multiple = true to indicate that we want to create a separate annotationdata entry (with the same key) for each of the matches (rather than have them together in one list).

[[elements.annotationdata]]
set = "https://ns.huc.knaw.nl/textannodata.jsonld"
key = "recipient"
value = """{{ $$./tei:teiHeader/tei:profileDesc/tei:correspDesc/tei:correspAction[@type="received"]/tei:rs[@type="person"] }}"""
skip_if_missing = true
multiple = true