Reconstruct 'google_ssl' to 'google_ssl_off'.
1. google_ssl is not flexible enough.
2. google_ssl_off is avaiable for any domains, it's much more useful than google_ssl.
document supplement
issue fixed #8, resolved #6
1. disallow all spider, if spiders crawling is needed, 'google_robots_allow on' will reset the allowance.
2. fixed the content-encoding problems of any 403 pages