support for non-fixed-width pattern look-behind

[yangcht]

I noticed that the current default re package does not support non-fixed-width pattern look-behind.

And this feature is actually very useful and powerful to have. For example, the following is not supported by re but by regex.
(?<=\/\*(\*(?!\/)|[^*])*\*\/(\s|\S)*\n)(?!\/\*(\s|\S)*\n)(.{120,})(?!(\s(?!\/\*)|\S(?!\/\*))*\*\/\n)

Is it possible to switch the default re to the regex package, which supports such a feature? I have issued a PR for it.

[yangcht]

sorry, clicked unassigned by mistake....

Now the PR has been split into two and ready for code review.