function shim(doc) {
            var a = -1;
            while (++a < elemsArrLen)
              // Use createElement so IE allows HTML5-named elements in a document
              doc.createElement(elemsArr[a]);
          }
addTest allows the user to define their own feature tests
the result will be added onto the Modernizr object,
as well as an appropriate className set on the html element

@param feature - String naming the feature
@param test - Function returning true if feature is supported, false if not