Currently, pandoc has hard-coded the following in order to make tight lists in
LaTeX:
```hs
text "\\itemsep1pt\\parskip0pt\\parsep0pt"
```
Which is fine, but does not allow customizations. For example, the `memoir`
class already has a `\tightlist` declaration for this purpose:
```tex
\newcommand{\tightlist}{%
\setlength{\itemsep}{0pt}\setlength{\parskip}{0pt}}
```
I'm proposing to use a similar solution:
```diff
@@ In Writers/LaTeX.hs:
-then text "\\itemsep1pt\\parskip0pt\\parsep0pt"
+then text "\\tightlist"
@@ In templates/default.latex:
+\newcommand{\tightlist}{%
+ \setlength{\itemsep}{1pt}\setlength{\parskip}{0pt}\setlength{\parsep}{0pt}}
```
This allows us to customize the tightness to our needs.
Backward Compatibility
If a person is using a custom LaTeX template (not based upon the `memoir`
class), the `\tightlist` declaration must be added.
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.
