Add Mocha and Jest under Unit Testing section

[Mocha][mocha-homepage] is a fairly well established alternative to
Jasmine for JS unit testing.

[Jest][jest-homepage] is new, and built "on top of" Jasmine. If that one
doesn't fit, I'm happy to amend the commit and remove it.

[mocha-homepage]: http://visionmedia.github.io/mocha/
[jest-homepage]: https://facebook.github.io/jest/