code-prettify

Setup:

<script src="https://cdn.rawgit.com/google/code-prettify/master/loader/run_prettify.js">

  The lang-* class specifies the language file extensions.
  File extensions supported by default include:
    "bsh", "c", "cc", "cpp", "cs", "csh", "cyc", "cv", "htm", "html", "java",
    "js", "m", "mxml", "perl", "pl", "pm", "py", "rb", "sh", "xhtml", "xml",
    "xsl".

https://github.com/google/code-prettify