embed REPL & canvas into teaching materials

Because CLJS is self-hosted (you can compile CLJS code using CLJS -- no JVM required), it is possible to have a webpage that runs its own REPL. Also, it is possible to embed Quil sketches in a webpage. So it should be possible to have a webpage with a REPL next to the Quil canvas that it controls.

The [Quil homepage](http://quil.info/) contains examples of sketches that run. You can [edit and run your own sketches online](http://quil.info/sketches/create), too.

The Quil creator has also written about understanding the CLJS self-hosting features:
http://nbeloglazov.com/2016/03/05/getting-started-with-self-hosted-cljs-part-1.html
http://nbeloglazov.com/2016/03/07/getting-started-with-self-hosted-cljs-part-2.html
(a third part hasn't yet been published)

Examples of webpages that include their own CLJS REPL:
https://github.com/Lambda-X/replumb
https://github.com/yetanalytics/re-pl

この issue ではリポジトリのファイルやテストが指定されていません。まず Quil のホームページとオンラインスケッチエディターを確認し、続いてリンクされている self-hosted CLJS REPL の例を確認してください。完了条件は、教材に、REPL の隣に Quil キャンバスがあり、そのキャンバスを REPL が制御するウェブページが含まれていることです。

索引モデルが issue の本文から書いたものです。