Log req.URL for panics

[Matt]

It would be really helpful, if we include the request URL in the error log message.
https://github.com/gocraft/web/blob/master/router_serve.go#L244

    ERROR.Printf("%v\n", req.URL)
    ERROR.Printf("%v\n", err)
    ERROR.Printf("%s\n", string(stack))

Also, I think we should combine those 3 single Printfs into one...

[Jonathan Novak]

Done