///
/// Generates `calc` function which allows mathematical expressions for a given property.
///
/// @author romamatusevich
///
/// @link http://caniuse.com/calc caniuse
/// @link http://www.w3.org/TR/css3-values/#calc spec
///
/// @param {String} $property
/// @param {String} $expression
///
/// @output
/// ```css
///   <property>: -webkit-calc(<expression>);
///   <property>: calc(<expression>);
/// ```
///
/// @example
///  .selector {
///    @include x-calc(width, "600px - 2em");
///  }
///
@mixin x-calc ($property, $expression) {
	#{$property}: -webkit-calc(#{$expression});
	#{$property}: calc(#{$expression});
}