Function to send an email using the simple Php mail() call. This is a very simplistic wrapper which is kept for its cuteness, but for no other reason than that.
Generic method to add an extra header. This method is now preferred over the depreceted 'add_header()' method above. We store our headers in an associative array, keyed on the proper-cased header name.
Return Printable Content Returns a printable version of the e-mail. Just returns the content as well as all the headers, and if for HTML, then it wraps it all in some (pre) tags. Useful for debugging.