Update the documentation to show when a parameter is a copy or a reference

When I look at the PHP core documentation I see when a parameter is a reference or not. (so we should review all our function documentation)

For example if you look at:
http://www.php.net/sort

Not only I know the type but also when it is a reference it is mentionned as &$array

I think we should do the same in our documentation, when I see our API with cas, for example:
http://www.couchbase.com/docs/couchbase-sdk-php-1.1/api-reference-retrieve-get.html#table-couchbase-sdk_php_get

it is not clear to me.