Parses a number or string representing margin sizes into an object. Supports CSS-style margin declarations
(e.g. 10, "10", "10 10", "10 10 10" and "10 10 10 10" are all valid options and would return the same result)
@static
@param {Number/String/Object} box The encoded margins, or an object with top, right,
bottom, and left properties
@param {String} units The type of units to add
@return {String} An string with unitized (px if units is not specified) metrics for top, right, bottom and left
function(box, units) {
            var a = this.addUnits,
                b = this.parseBox(box);

            return a(b.top, units) + ' ' +
                   a(b.right, units) + ' ' +
                   a(b.bottom, units) + ' ' +
                   a(b.left, units);

        }