How should the micro-addon work at build time

[begedin]

While writing the PR description for the ember-cli feature, I started to reconsider how micro-addons should work.

How it works now

Currently, the files are copied from a flat file structure in such a way that the following happens:

• components are accessible via import MyComponent from 'app-name/components/my-component';
• libraries are accessible via import MyLibrary from 'app-name/lib/my-library';
• helpers are accessible via import MyHelper from 'app-name/helpers/my-helper';

There are 3 addon hooks we use to make this work:

• treeForApp copies and renames component.js, helper.js, library.js
• treeForAddon copies style.css (for components)
• treeForTemplates copies template.hbs

I think this might not be 100% according to convention and where they're accessible from fells a bit illogical.

How I think it should work

• treeForAddon should copy all of them into addon/[type]/addon-name.[extension]
• treeForApp should create the standard import-export modules for components and helpers, so they are also directly accessible from the app. Libraries should be importable from the addon only, so they do not require import-export modules.
• treeForApp might be able to create a template, but if that is impossible, then treeForTemplates should still be used for that

I think this would follow convention more closely.