Implement inline precompilation.

[rwjblue]

• Bring initial implementation over from ember-cli-htmlbars-inline-precompile.
• Refactor to avoid duplication, streamline both .hbs transpilation and inline precompilation
• Add CI run to ensure there is no conflict with ember-cli-htmlbars-inline-precompile
• Add smoke tests ensuring that importing from all three known paths works

Allows consumers to use inline precompilation without having
ember-cli-htmlbars-inline-precompile as a dependency. Example usage:

import { hbs } from 'ember-cli-htmlbars';

export default Ember.Component.extend({
  layout: hbs`wheeeee`,
});

Implements ember-cli/ember-cli-htmlbars-inline-precompile#298