Add NumberSpan definition (non-DTD, but applies to enough to be useful). All widely used non-deprecated attributes have been implemented (except for rel/rev, but that's tricky). Add note about quirky COL handling and possible implementation of a workaround.

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@174 48356398-32a2-884e-a903-53898d9a118a

tests/HTMLPurifier/Strategy/ValidateAttributesTest.php

@@ -80,6 +80,9 @@ class HTMLPurifier_Strategy_ValidateAttributesTest extends
         <td abbr="carrot">Carrot Humungous</td>
         <td>$500.23</td>
     </tr>
+    <tr>
+        <td colspan="2">Taken off the market</td>
+    </tr>
 </table>
 HTML;
         $expect[13] = $inputs[13];