Use regexpu for regular expression transpilation

[mathiasbynens]

See https://github.com/mathiasbynens/regexpu. You can use this as a dependency for your transpiler to add support for the ES6 /u flag for regular expressions.

(Traceur and 6to5 depend on regexpu as well, FWIW.)

[army8735]

thx, I will take time to do it

[mathiasbynens]

There is now a separate module for just the regular expression rewriting logic: https://github.com/mathiasbynens/regexpu-core