A polyfill for the ES6 Set object, allowing you to use that Set object in any browser from IE7 on up.

When you're running in a newer browser that supports the ES6 Set object, the polyfill will get out of the way
and you will just be using the native object directly.

Since the ES6 specification is not yet finalized, this implementation is based on the 4-27-2014 draft of the
ES6 specification.  The test page is compatible with both the polyfill and the native Set implementation in Firefox 29.

This is a polyfill so it test the environment to see if a fully capable Set object is already present.  
As of 5/21/2014, the only browser that has such a Set object is Firefox.  IE11 contains a Set object,
but it has no way of iterating the keys of the Set object so the polyfill replaces it to offer full
functionality.

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You only need to read this info below if you're trying to use this polyfill in IE7 and IE8...

If you intend to use this implementation in IE7 or IE8, then you cannot use the ES6-specified .delete() method
directly because IE7 and IE8 flag the "delete" method as a reserved keyword and any code that tries to use it
causes a parse error.  This can be worked around by either specifying the delete method as a string as in:

// this works in IE7 and IE8
mySet["delete"](5);

instead of the more traditional:

// this can't be used in IE7 and IE8
mySet.delete(5);

Or by using the non-standard .remove() method which has been included in the polyfill for work-around purposes.  
Of course, the .remove() method does not exist in the ES6 native Set implementation so if you want to
use .remove() for max compatibility, then your code needs to install .remove() on the native Set
implementation.  That can be done by including this code to add a .remove() alias:

;(function() {
    // if no .remove() method, add one
    if (!Set.prototype.remove) {
        // define a .remove() synonym for .delete()
        // so we can use it in our test code that has to also run in IE8
        Set.prototype.remove = Set.prototype["delete"];
    }
})();

So, if using this extra method definition, then you can just use:

mySet.remove(5);

instead of:

mySet["delete"](5);