Add queryParams to request object

This adds a `queryParams` to the request object that is passed to the handler function. This is useful if you want to use the URLs query string parameters inside your handler function.

USAGE / TEST:
````
test("queryParams are passed", function(){
  var params;
  pretender.get('/some/path', function(request){
    params = request.queryParams
  });

  $.ajax({url: '/some/path?zulu=nation'});
  equal(params.zulu, 'nation');
});

````