Reassigned EchoJS as an engine, not an ES6->ES5 compiler.

Closes #362. Note that this commit does not change es6/index.html, to avoid merge conflicts with my other pull requests. A fresh compile should be done after all of them are accepted.
Merge pull request #365 from webbedspace/ejs

Reassigned EchoJS as an engine, not an ES6->ES5 compiler.