Decouple the *-matcher and *-mapper libraries.

 Earlier, the -matcher libraries used the -mapper libraries
 directly, to get results directly from the DOM, but now these two
 steps of the search has been completely separated, so this is no
 longer necessary. The end result is that now the matcher library
 only needs a way to access the corpus, and nothing else.

 As part of this, I have removed all wrapper functions, which was
 placed on the -matcher layer earlier only to wrap the -mapper layer.

 Now these are called directly on the -mapper layer.

 Furthermore, the matcher library is now completely mapper independent,
 so I can get rid of the separate ancestor and mapper-specific descendant
 classes.

 The library is still called dom-text-matcher, but now the
 name is just a legacy; it's not touching the DOM at all.

 (In the process, I also removed the unused and broken feature to
 limit search to a DOM subtree.)

 Also, there were some small internal bugfixes.
Merge pull request #1 from hypothesis/multipage-2

Decouple the *-matcher and *-mapper libraries.

All the stuff required for PDF.