new json export format

The new format uses arrays for all subfield values,
not just for those, which had more than one element.

    old: {"020": [{"a": "9781234567890", "ind1": " ", "ind2": " ", "z": ["A", "B"]}]}
    new: {"020": [{"a": ["9781234567890"], "ind1": " ", "ind2": " ", "z": ["A", "B"]}]}

This unifies and hopefully simplifies processing on the consumer side.

Control field values are still just strings, since they are single values by spec.
v1.5.0
build deb with version and arch
Merge remote-tracking branch 'origin/master'
updated Makefile