getStats() documentation states incorrect parameter options

The documentation for the getStats() function states that parameters may be passed to the function to filter the list of returned statistics (e.g. by statistic name). The functions as implemented however ignore any such parameters, and this is in line with the behavior of the pecl-memcached extension as desired (c.f. http://www.php.net/manual/en/memcached.getstats.php). In other words, the parameters information given in the docs should be removed as the implied filtering capabilities do not exist.