Binary upgrade, fixes #85

This PR contains couple of features:

* Simple support for live binary upgrades
* Remove misleading connwatcher that does not work properly
* Track connections to sockets and emit stats 
Another way of writing this:

    switch curr {
    case http.StateNew, http.StateIdle, http.StateActive:
        c.inc(conn, cur, 1)
    }

Though inc checks for the same states anyway. What do you think of just calling inc unconditionally?