Fix path to stylesheet in demo page
Clearfix grid container instead of using overflow:hidden

* Add silent placeholders for clearfix
* As clearfix uses pseudo elements, the overlay grid lines (that also
used pseudo elements) won't work so they've been removed.
* Remove extra arguments in call to generate-grids in demo stylesheet
Remove refs to overlays and legacy args from documentation
Merge pull request #2 from guyroutledge/remove-overflow-hidden

Overflow hidden can cause clipping issues