Add option to use shlex.split with split_args_with on @botcmd

This is useful for plugin authors who need to accept multiple arguments
but have input that may contain spaces. This will allow the arguments to
be quoted just like on a unix shell.

This is also directly implemented now in the !room_topic and
!room_occupants commands, which prepares them for easy input of HipChat
room names (which may contain spaces).