Feature suggestion: Smarter handling of <code> block languages

[bland328]

markdownizer-chrome is fantastic, thank you!

It would be even more fantastic if it could be smarter about the language of code blocks.

For example, when I use it to copy the Python code block in this Stack Overflow answer, I get:

```hljs
>>> import codecs
...

It would be lovely if markdownizr would dig a little deeper into the <pre class="lang-py s-code-block"> tag, so that it could generate:

```py
>>> import codecs
...

If I get a chance to tackle it myself one of these days, I'll send a PR. Thanks for considering!