Reveal implementation flaws of completeness metric

I have written two tests to demonstrate the inherent implementation
problem of the completeness metric.

(1) The metric does not take subfields into account if the main field
    is empty, hence records with fewer main fields might score higher.

(2) It sums subfields instead of averaging them. This way a record
    having more items which again are hashes might score higher than
    a record with fewer items.

In the next step I am looking forward to make these tests green by
improving the implementation.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>