Everything builds! 🎉

The headline feature: ember serve and ember test and ember build all work properly now, across platforms. And builds are much faster on all platforms, too.

Miscellaneous other changes:

• Updated the base type definitions in app/config/environment.d.ts to include the defaults generated when creating an Ember app (thanks, @luketheobscure!)
• Cleaned up the internals a bit
• Updated the README with clearer installation instructions and notes on using the add-on to develop other add-ons