Rearrange style guide files and add additional samples
Polish base screen.less
Replace multiple slashes with single slash
Allow fill mixin to accept a color value
Allow $css and $prop to accept a callback function taking the element, index, and existing property
Allow $val, $width, and $height to accept a callback function taking the element, index, and existing value
Allow $wrap and $wrapInner to accept a callback function taking the element and index
Update readme
Update beta release build to 10