Improve code snippet preview

[adangel]

In order to copy the code snippet, it would be useful to

• have a copy-to-clipboard button
• render the snippet with line numbers in a table, so that the code without the linenumbers can be selected easily. the problem:
  

Github renders this as a table, and the selection is easy:

So, we probably should not render the snippet as a single pre, but as e.g.

<table>
 <tr>
   <td>263</td>
   <td><code>         for (int i = srcBegin + (1 >> LO_BYTE_SHIFT); i < srcEnd; i += 2) {</code>
 </tr>
 <tr>
   <td>264</td>
   <td><code>             dst[dstBegin++] = value[i];</code>
 </tr>
 <tr>
   <td>265</td>
   <td><code>         }</code>
</tr>
</table>

[adangel]

Also I noticed, that the highlight doesn't work anymore....