The 30s hardcoded readTimeout in Pipe() caused all CONNECT tunnel
connections to be hard-closed after 30s of inactivity, breaking
WebSocket and long-polling connections through the proxy.
Pipe() now accepts a WithReadTimeout(d) option. When d is 0 (the
default) no read deadline is set, relying on TCP keepalives or context
cancellation to detect dead connections instead.
The HTTP handler exposes this as the idleTimeout metadata key.
Fixes: https://github.com/go-gost/x/issues/91
Andrew Beresford
290e9c37d5