Two new ClojureScript examples: jsinterop and boids

Added to new examples. One shows an example of using any old JavaScript library from ClojureScript using [mrhyde](https://github.com/dribnet/mrhyde). The other is a boids simulation, which also leverages the interop abilities of [strokes](https://github.com/dribnet/strokes).

Both include live web demos (though it would probably be better to move these to the web site for the book for publication). They are also both a little long, but I can help whittle them down if they are otherwise friendly to being included.