Add syntax-highlighting to code samples on ReactiveX web pages

[DavidMGross]

I'm not sure if we can leverage something in the CSS / site generation we're already working with or if we'd need to pull in some additional CSS/JS to make this work.

Most of what is in the operator pages, including the sample code sections, is in HTML rather than markdown, although those pages go through the markdown->html generator like the rest of them, so maybe we could leverage that.

The code sample sections are currently marked with <div class="codelanguageName"> in anticipation of being able to accomplish this at some point.

[flatmap13]

Perhaps we can use the code snippets mechanism that I've added in the snippets branch for this? This was mentioned in #99, I'm also working on the improvements that @samuelgruetter suggested.