Add RegExp function for Replace Rule

Support "g" and "i" flag

For example:

Replace
/^http:\/\/([^\.]+\.)?abcd\.com/
With
http://www.1234.com
Will replace www.abcd.com, abc.abcd.com, abcd.com with 1234.com

Replace
/\w{4}-(efgh)/
With
1234$1
Will replace abcd-efgh.com, aaaa-efgh.com with 1234efgh.com

Glitch:
All occurrences of the matching string will get replaced even if "g" flag is not specified.