Referencable codeblocks

Hi, first of all, thank you for this project, it is a great tool to save precious time.

I would like to ask a new feature: referencable fenced code blocks.

When a fenced code block is translated into latex, it has neither a caption nor a label.

I solved this by using this hack, which includes those two latex parameters into the `lstlisting` command arguments:

```
\```Ruby,label={such_code},caption={Very\,listing}
puts("WOW")
\```
```

> backslash are needed to escape GitHub markdown fenced code blocks.
> `\,` inserts a space in latex, as whitespace would stop the parsing of the code language

You can reference the code using `[](#such_code)`.

I hope that this helps, best regards, tux_mind.