The code:
~~~{#test}
asdf
~~~
gets compiled to html:
<pre id="test">
asdf
</pre>
So it is possible to link to the identifier `test`
But this doesn't happen on latex
When using the listings package (`--listings`) it is possible to set the
identifier using the `label=test` property:
\begin{lstlisting}[label=id]
hi
\end{lstlisting}
And this is exactly what this patch is doing.
Modified LaTeX Reader/Writer and added tests for this.
