Support display: grid and inline-grid

New grid layout box model
http://dev.w3.org/csswg/css3-grid-layout/#grid-containers
landed in IE10 and will probably come with Chrome 27.

This adds new display property values 'grid' and 'inline-grid'
(and maybe later 'subgrid') that need to be prefixed.
Merge pull request #146 from ThomasWeiser/gh-pages

Support display: grid and inline-grid