switch to highlight.js for code highlighting

[duncdrum]

see the related issues here and here
the current code highlighter is ancient and preventing updates to jquery. Switching to an external js library for code-highlighting should help us in the long-run.

[adamretter]

@duncdrum Do you want to add some of these to the community call agenda, so that they get the attention they deserve?

[duncdrum]

I have updated the highlight.js xquery parsers. It works within my test build of the documentation app, and passes their tests. However, their Travis is complaining so we ll see how that goes.
Once, this PR highlightjs/highlight.js#1649 is accepted, we should upgrade in various apps

[duncdrum]

[duncdrum]

more samples from tuning.xml

direct xml markup is now properly capture, so is computed constructor syntax, still a few corner cases remain

[duncdrum]

see d1d43c1