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.