Switch from net.Conn to *net.TCPConn

- Switch from an interface to a struct pointer in the rwTimeoutConn
  wrapper. In extreme cases, the interface overhead may be up to 5%
  (though it's probably very close to 0% at normal network speeds).
  Since http is only a TCP protocol, we don't need the net.Conn
  abstraction anyway.
Merge pull request #15 from jbardin/TCPConn

Switch from net.Conn to *net.TCPConn