`columns`

Add polyfills for non supported values (ie: `break-before/after/inside` with `-webkit-column-break`, etc.)
Add resettable values to `reset` (#4)

Reference:
- http://www.w3.org/TR/css3-multicol/
- https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Using_multi-column_layouts
- http://caniuse.com/multicolumn
- http://dev.opera.com/articles/view/css3-multi-column-layout/
-https://github.com/chriseppstein/compass/blob/stable/frameworks/compass/stylesheets/compass/css3/_columns.scss