Implement document matching method from MASSALIGN

[maltebo]

The method can be found in the MASSALIGN paper on page 2. Improvement on currently used methods: Allows not only n-1, but also 1-n-matchings, looks (more?) at the vicinity.

[maltebo]

This should work with the same parameters as the other two implemented document matching algorithms, i.e., on the similarity matrix, and with a threshold/sd_threshold (should not be 0 for this method!)