Add internal documentation building via YUIDoc

Run `npm run docs`

Taken directly from Ember.js with minor changes, with exception that
generator will also create HTML docs as well as JSON data. We can fall
back on this until the ember-cli.com site includes this API
documentation.
Add doc signatures for EmberApp

Extremely minimal doc comment blocks. Not yet qualified to complete.
Add documentation about documentation
Allow addons to inject middleware into testem

This PR depends upon https://github.com/airportyh/testem/pull/410 being
accepted

Primarily the use case is with any addon that injects a middleware into
the ember server's, this will allow addon authors to also expose that
middleware through `ember test` if/when noted PR above is accepted by
@airportyh
Merge pull request #2128 from bcardarella/bc-support-testem-middleware

Allow addons to inject middleware into testem
Fix description for service-test
Merge pull request #2235 from jonnii/bug/spelling-error

Fix description for service-test
Add a few more content-for placeholders.

* Add `{{content-for 'body'}}` to `app/index.html` and
  `tests/index.html`
* Add `{{content-for 'test-head'}}` to `tests/index.html`
* Add `{{content-for 'test-body'}}` to `tests/index.html`
Merge pull request #2236 from rwjblue/content-for-sprinkles

Add a few more content-for placeholders.
if the error has an error.file, display it.
Merge pull request #2237 from stefanpenner/error-file

if the error has an error.file, display it.
Refactor: Add Multiple bower packages in one statement

Remove unnecessary semicolon

Add tests for addBowerPackagesToProject

Properly test addBowerPackageToProject
Merge pull request #2222 from peterchoo/addBowerPackages

Refactor: Add Multiple bower packages in one statement
Add multiple npm package install support + tests
Merge pull request #2245 from peterchoo/addPackagesToProject

Refactor: Allow multiple npm packages to be added at once + tests
Update broccoli-static-compiler.

Fixes a symlinking related regression that prevented the use of
`destDir` of `/` without a `files` glob array.
Update broccoli-asset-rev.
Merge pull request #2250 from abuiles/update-assets-rev

Update broccoli-asset-rev.
Merge pull request #2248 from rwjblue/update-static-compiler

Update broccoli-static-compiler.
ensure line + col information is also displayed