!!!lang code blocks should set the lang in <pre>'s class.

[dominikh]

Right now, there is no way to tell which language a code block contains after it has been processed by YARD. This makes it hard to postprocess the output.

Methods in YARD::Templates::Helpers::HtmlHelper that might needs adjustment:

• #html_syntax_highlight
• #htmlify

[FranklinYu]

What is this about? Is this about hinting about the syntax of a code block in RDoc? So

!!!bash

    apt-get update

in RDoc is equivalent to

```bash
apt-get update
```

in Markdown?

[lsegal]

@FranklinYu Indeed, except the bang needs to be indented at the same level as your markup:

    !!!bash
    apt-get update