Stringifies an object into one string with every pair separated by `&`

@method _toQueryString
@param data {Object} containing key-value pairs
@return {String} stringified presentation of the object, with every pair separated by `&`
@private
function(data) {
            var paramArray = [],
                key, value;
            for (key in data) {
                value = data[key];
                key = ENCODE_URI_COMPONENT(key);
                paramArray.push((value === null) ? key : (key + "=" + ENCODE_URI_COMPONENT(value)));
            }
            return paramArray.join("&");
        }