Manage members of a group.
$group = new Bitbucket\API\Groups();
$group->setCredentials(new Http\Message\Authentication\BasicAuth($bb_user, $bb_pass));
$group->members()->all($account_name, $repo_slug);
$group->members()->add($account_name, 'developers', 'steve');
$group->members()->delete($account_name, 'developers', 'miriam');