Autotiling 1.8

• added -l LIMIT, --limit LIMIT argument; #41 by @Syphdias

It limits how deep will autotiling work; try -l 2, if you like master-stack layouts; default value is 0 (no limit); avoid the 1 value, that will actually spoil autotiling. Below the level you specified, stacking and tabbed layout will behave well again.