Add basic support for CC and BCC

This may not be how you want to implement it, but I added some basic support for CC and BCC, since the main SendWithUs gem supports them and this one currently doesn't. (And I need them.)

The way I've done it, the API is a bit fiddly, so you may have a better idea to handle the array of names and addresses. This way you need to pass something like:

    :bcc => [{:address => "name@example.com"},{:address => "name2@example.com"}]