Static scope analysis and transpilation of ES6 block scoped const and let
variables, to ES3
Node already supports `const` and `let` so you can use that today (run
`node --harmony` and `"use strict"`). `defs.js` enables you to do the same
for browser code. While developing you can rely on the experimental support
in Chrome (chrome://flags, check Enable experimental JavaScript). `defs.js`
is also a pretty decent static scope analyzer/linter.
