Add sendUtf8 method to socket objects.

Add sendUtf8 method to socket objects.

Encoding UTF-16 (the native string representation) to UTF-8 is rather
expensive, however just chopping off the second bit to convert UTF-16 to
ASCII is rather fast. I've noticed major performance issues with
String::WriteUtf8 and thus I'm going to explicitly separate in the API.

Still need interfaces to this for the web server.