wemux was killing the currently selected server as the $wemux prefix is not rebuilt during the stop command.
`wemux list` outputs a list of all running sessions prefixed with a number. `wemux join` and `wemux stop` can now be invoked with this number. `wemux join 3` or `wemux j 3` would join the third server on the list. `wemux stop` can now be passed either the number, or the session name. If no argument is passed it will default to stopping the current session.