Ability to include some document structure in the hits results

[jan-niestadt]

It would be nice if, for example, certain XML tags like <s/> would be included in the hits concordances.

Right now this can be achieved, by passing usecontent=orig, but this uses the content store and is pretty slow as a result. Better would be if we could get this information from the forward index (or a similar datastructure in the index).

We should probably take this into account when looking at treebank-like structures (see BARK 10).