Don't have any known features in the 3.3 release.
Better documentation for the has_feature? method.
Allow plugins to expose their features too.

Plugins can call Sass.add_feature(feature_name) to expose their features
and in doing so get the same feature detection benefits that Sass itself
gets from this capability. Plugin features must begin with a dash to
distinguish them from official features and ensure our namespace is not
polluted.