Add feature: approximate (fuzzy) matching

[RaiKoHoff]

We decide to use Onigmo to be the regex search engine for Notepad3. It has been the winner among several other candidates.
Some of these candidates had a nice feature, called approximate matching.
For example TRE or Intel's Hyperscan.

Maybe this might be a nice feature for Onigmo too?

(The dark side: There is generally a performance impact associated with approximate matching due to the reduced specificity of the matches. This impact may vary significantly depending on the pattern and edit distance.)