Implement a `matchQuote` function which will be used to replace
`dom-anchor-text-quote` for finding the best match for annotation quotes
in the document text.

The new implementation is based on the `approx-string-match` library and
provides several improvements over the existing one:

 - Better performance when there are many differences between the quote
   and closest document text

 - It will be easier for us to tune the degree of mismatch allowed
   between the quote and document text and how candidate matches are
   ranked