Move away from `broccoli-dist-es6-module`.

Instead, use `broccoli-es6-module-transpiler`, which supports the latest
version of the ES6 module transpiler. Rather than generating separate
distributions for `amd`, `cjs`, `named-amd` and `globals`, we now output
a single "bundle" format.

The inspiration for this was taken from rsvp.js:
  https://github.com/tildeio/rsvp.js/
Deprecate `selectedIndex`, use `selected-index` instead.
Version bump to 0.3.0.