Display: inline-block for column layout

This is only something I though you may want to think about. Please, just ditch this PR if it doesn't sit well with you.

This commit replaces float:left with display: inline-block as the method for
alligning the grid elements. I have recently switched to using this method because, as inline-block does not collapse the parent element, there is then no need to clearfix the elements,
reducing the output.

To me, it also feels a little cleaner, as floats aren't really intended for layout. 

Since making the switch I've found my life a lot easier :)

The only gotcha; this doesn't work as intended in IE7/6 (what does?) though it can be hacked of course http://blog.mozilla.org/webdev/2009/02/20/cross-browser-inline-block/