Another regex impl: regress

[robinst]

There's a new pure-Rust regex implementation that supports backtracking: https://github.com/ridiculousfish/regress

It might be interesting to add it as another regex impl (in addition to onig and fancy-regex) and see if it supports enough of the required syntax to be usable for syntect!

CC @ridiculousfish

[trishume]

Yah I saw it and thought about that too. Especially with your refactor to separate regex engines into a module it would be much easier to try it out.

The biggest thing that may or may not be an issue is differences between Oniguruma syntax and features and ECMA syntax. For all I know most of the syntax and supported features could be the same or they could be very different, I haven't looked into it. It may be possible to paper that over with rewriting or upstream PRs though.