Don't generate @since tags when versions data not available.

    # Loads in exported docs and generates @since tags based on that data.

    def import(versions, relations)

      if versions.length > 0

        generate_since_tags(read_all(versions), relations)

      end

    end

    # Reads in data for all versions, returning array of

    # version/class-data pairs.  We don't use a hash to preserve the