Add syntax highlighting with builtin parser

I have included `highlight.js` to introduce the option of syntax highlighting with the builtin parser.  The css is from the [highlight.js source][ref1] and it github flavored.

I also made a few changes to the sample.md file to reflect these changes, as well as to include an example of the MathJax function.

[ref1]:[https://github.com/isagalaev/highlight.js/blob/master/src/styles/github.css]