Allow setting 'raw' attrs on XML for tables to be loaded from hex

Previously one had to set the 'ERROR' attribute.  Accept raw also.
So, for example one can say:

  <cmap raw="1">
    <!-- Hand-coded format13 table mapping all Unicode
         characters to .notdef glyph. -->
    <hexdata>
      0000 0001 <!-- version numTables -->
        0000 0006 <!-- platformID encodingID -->
        0000000C  <!-- offset -->
          000D 0000 <!-- format reserved -->
          0000001C  <!-- length -->
          00000000  <!-- language -->
          00000001  <!-- nGroups -->
            00000001  <!-- startCharCode -->
            0010FFFE  <!-- endCharCode -->
            00000001  <!-- glyphID -->
    </hexdata>
  </cmap>