Fix on_part message handler

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>
Add auto-join on invite handler

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>
Check event.arguments lenght for kick and invite handlers

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>