Implement io.ReaderFrom/WriterTo for Conn
Implement io.ReaderFrom/WriterTo for Conn

This change increase performance when proxying wrapped connections using io.Copy.
Since go 1.11 copying between tcp connections uses the splice system call on linux yielding considerable performance improvments.
See: https://golang.org/doc/go1.11#net

Signed-off-by: Fabian Ruff <1fac0fca3b70815c19f1e1d7aa60d65991d4559b@sap.com>

pires/go-proxyproto