Add provided classes to wrapper div

[duckwork]

With a source like this:

``` {.python .numberLines}
if is_true:
    pass
```

pandoc generates

<div class="sourceCode" id="cb1"><pre class="sourceCode python try"><code class="sourceCode python"><a class="sourceLine" id="cb1-1" title="1"><span class="cf">if</span> is_true:</a>
<a class="sourceLine" id="cb1-2" title="2">    <span class="cf">pass</span></a></code></pre></div>

I'd like the enclosing <div> to include the classes I've specified in the source (or at least python.) I'm thinking of changing the style of different code blocks based on which language they are.

I've traced the issue to skylighting, in the formatHtmlBlock function. I think all that's needed is a change in the first line:

  H.div ! A.class_ (toValue "sourceCode") $

to

  H.div ! A.class_ (toValue $ Text.unwords classes) $

I'm writing this as an issue to see if there'd be interest in a pull request for this change.

[dbaynard]

The div is only there to fix a spacing issue. Can you just change the style of the pre?

[duckwork]

The issue comes in when adding background colors. Say I want to color all python blocks as blue and all bash as green, while everything else is black. Currently, it looks like this jsfiddle. With the proposed change, it'll look like this one. Note how in the first fiddle, also, the code lines are only highlighted to the end of each code line.