Syntax highlight now also for Markdown code blocks

I noticed the website doesn’t apply syntax highlight to posts with their code inside ``` instead of <code> tags.
Looking at the code, seems like only <code> tags were being searched for and replaced. But not anymore!

P.S.: @DTrejo, I just noticed on the README.md that you asked for help regarding this issue… after developing this and going to submit this pull request. Talk about serendipity… :D