Split multiple values in the same column and create an object for each.

For example given a csv with the following content:
id, documents
0 , foo.pdf, bar.pdf, baz.pdf

and a mapping
{'attachments': [{'uid': 'list:documents'}]}

will result in
{'attachments': [{'uid': 'foo.pdf'}, {'uid': 'bar.pdf'}, {'uid': 'baz.pdf'}]}