Migrate to re2

[PhilippMDoerner]

The regex lib appears to have deprecated its re/RegexMatch/Regex API in favour of something more macro based (?).
The API is identical, but the types and symbol-names are different.

You notice this if you use regex-routes in prologue, as you now get these warnings:
Warning: use re2(static string) instead; re is deprecated [Deprecated]

Now they're re2/RegexMatch2/Regex2. I did 5 minutes of playing around and it seems this will require adjusting a few things. The few I could think of:

• Adjust exports of core/basicregex.nim
• Adjust addRoute proc in core/applications.nim
• Adjust initRePath proc in core/route.nim