Make it possible to join indexed fields into an array of objects.

Example: a CSV with

foo_0_bar  foo_1_bar
Hello      Bye Bye

Can be transformed into
[{'name': 'Hello'}, {'name': 'Bye Bye'}]

via the mapping
[{'name': 'foo_#_bar'}]
Merge pull request #25 from florianpilz/master

Make it possible to join indexed fields into an array of objects.