Make sure you have downloaded the latest google-api-php-client (https://github.com/google/google-api-php-client appears to be the authoritative source now). There was a change intoduced with XE8 that was incorporated into version 0.6.6 which enabled sharingFeatures - 0.6.6 is the minimum version necessary for these features, and it is part of the QuickStart example. (Note that there have been some changes in the 1.0 client, but they are mostly naming changes. See https://developers.google.com/api-client-library/php/guide/migration for details about the changes.)
I'm not quite sure what you're asking about acceptCommands. In PHP terms, this should be an array of arrays. (Or a numeric based array, each consisting of associative arrays mapping from a string (currently the value "type") to a string (either the strings "TAKE_A_NOTE" or "POST_AN_UPDATE").
I haven't tested this, but if you wanted your contact to work with both voice commands (for example), you should be able to use code something like this:
$acceptCommands =
array(
array("type" => "TAKE_A_NOTE"),
array("type" => "POST_AN_UPDATE")
);
$contact->setAcceptCommands( $acceptCommands );