Add support for Chapel?

[bradcray]

As a Chapel developer, it would be very helpful to me if Google's code-prettify supported highlighting of Chapel code so that I could make use of it in my StackOverflow questions and answers. This issue is requesting the addition of such support.

[bradcray]

[A proposed implementation has been offered in PR #518 by @victor-ludorum, but seems to be in PR limbo. I'm filing this issue in hopes of moving it forward, if possible.]

[ben-albrecht]

There are 2 open PRs for Chapel which we ought to resolve before pinging a reviewer:

• Add chapel language support #588 (by @krishnadey30)
• Add Chapel to the list of supported language #518 (by @victor-ludorum)

@krishnadey30 and @victor-ludorum -- do either of you feel like championing this such that we can close the other PR?