Add various Match.merge(Match) functions

[lukaseder]

Maven has a set of specifications on how to merge / append two similar configuration elements, e.g.

<x>
  <a/>
  <b x="1"/>
</x>

<x>
  <b x="2"/>
  <c/>
</x>

The output of such a merge operation could be, for example:

<x>
  <a/>
  <!-- Preserve first on conflict -->
  <b x="1"/>
  <c/>
</x>

Or:

<x>
  <a/>
  <!-- Override first on conflict -->
  <b x="2"/>
  <c/>
</x>

Let's look at Maven and re-implement some of their algorithms.