Automatically optimize regexes

[eteran]

After I complete the regex engine refactor, I'd like to have it be able to optionally optimize the regexs by performing transformations similar to the ones found here:

https://bisqwit.iki.fi/source/regexopt.html

I've in the past done some experiments where we can trivially replace things like [0-9] (which gets expanded to [0123456789]) just a \d which is much more efficient in both time and space.

This is a low priority for now since we're pushing for "fix all quirks and get NEdit 6.0 released", but I wanted to keep this on my radar.

[tksoh]

This looks interesting. Let's get 6.0 out of the door ASAP! ;-)