/// Calculate width for a flow column
///
/// @author [@esr360](http://twitter.com/esr360)
/// @access public
/// @group Kayzen-GS
/// @param {number} $span - the width (in columns) of returned value
/// @param {number} $columns - the maxinum number of columns being used
/// @return {number} - width of column
@function kgs-flow-width($span, $columns) {
    @return ((100 / $columns) * $span) - kgs-option('gutter');
}