details about modifing marked lib

[layerssss]

what is the reason?

[qiao]

The original marked library tends to wrap the colorized code snippets into a <p> element, which is not desired.

Before:

```python
print 1

After pygments:

``` html
<div class="highlight">
  <pre>
    <span class="k">print</span> <span class="mi">1</span>
  </pre>
</div>

After marked:

<p>
  <div class="highlight">
    <pre>
      <span class="k">print</span> <span class="mi">1</span>
    </pre>
  </div>
</p>

Notice that the <p> wrapper is superfluous. So I modified marked to suppress this behavior.