Span Class Prefixing

I believe I prefixed all the span classes with the `hljs-`. If the class wasn't in classref.txt then I missed it, but this is the prefixing needed to prevent class collision.

And just for those curious about the script I use to transition the 32 styles, [I put it in a gist][1].

[1]: https://gist.github.com/sourrust/7493847