Fix bug with docutils' code directive.

Since version 0.9 `docutils` supports `code` directive. But this directive
can generate fullname classes for the `pygments` style classes.

For example, the following code

```reStructuredText
.. code:: c++

    GetFoo()->do_something();
```

generate the following output

```html
<pre class="code c++ literal-block">
  <span class="name">GetFoo</span>
  <span class="punctuation">()</span>
  <span class="operator">-&gt;</span>
  <span class="name">do_something</span>
  <span class="punctuation">();</span>
</pre>
```

Note, that fullname classes were used, when we need a short one

```html
<pre class="code c++ literal-block">
  <span class="n">GetFoo</span>
  <span class="p">()</span>
  <span class="o">-&gt;</span>
  <span class="n">do_something</span>
  <span class="p">();</span>
</pre>
```
Merge pull request #710 from ikalnitsky/code-directive

Fix bug with docutils' code directive.