pass a keyword argument to circuit_closed, circuit_failed, stream_detach, stream_closed and stream_failed
fix up comments
remove unused code
issue #18: provide all flags with events

For several circuit and stream events, Tor may provide several flags (acutally
an unbounded number of flags) and previously only "REASON" was provided (as a
reason kwarg). Now, all flags are provided with both upper-case (as from Tor)
and lower-case versions, to facilitate method-signatures with the flags one
is interested in.