Add table pretty printing & alignment

Also dismissed implementing colgroups for now - had it but didn't like the
added complexity for a very questionable benefit - i've actually never used
that feature of org tables...

org/testdata/footnotes.html

@@ -53,13 +53,16 @@ and tables
 <table>
 <tbody>
 <tr>
-<td>1</td><td>a</td>
+<td class="align-right">1</td>
+<td>a</td>
 </tr>
 <tr>
-<td>2</td><td>b</td>
+<td class="align-right">2</td>
+<td>b</td>
 </tr>
 <tr>
-<td>3</td><td>c</td>
+<td class="align-right">3</td>
+<td>c</td>
 </tr>
 </tbody>
 </table>