Add support for regex_replace

Just a feature request! I'm using your library to take the place of what appears to be non-working C++ standard regexes in the Android NDK. Unfortunately, I was also using calls to `regex_replace`, which don't seem to have an equivalent in this library.

The functions are detailed here:

http://en.cppreference.com/w/cpp/regex/regex_replace

Thanks for the great work on the library!
