Add support for respawn-pane #9

respawn-pane [-k] [-t target-pane] [shell-command]
              (alias: respawnp)
        Reactivate a pane in which the command has exited (see the remain-on-exit window option).  If shell-command is not given, the command used when the pane was created is executed.  The pane must be already inactive, unless -k is
        given, in which case any existing command is killed.