Fix charset_types as mime.types is updated

The default Nginx `charset_types` [1] is 

    text/html text/xml text/plain text/vnd.wap.wml application/x-javascript application/rss+xml

Since the `mime.types` is updated and `application/javascript application/json` are now being used instead of `application/x-javascript`, if the `charset_types` is not updated, then `charset` directive will not work as expected.

Besides, I have added `text/css` for better handling of non-ASCII in css file. [3]

[1] http://wiki.nginx.org/HttpCharsetModule#charset_types
[2] http://forum.nginx.org/read.php?2,52360,52370#msg-52370
[3] http://trac.nginx.org/nginx/ticket/312