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
try clearing npm cache on appveyor build
this shouldn't work
more bad ideas
node on windows should be outlawed
Mention the possibility of top-level errors until testem reports this
Merge pull request #2216 from joostdevries/improve-error-message-notests

Mention the possibility of top-level errors until testem reports this
Give clear error when failing to read config from meta
Allow filtering tests run through testem.

Adds `--filter` command line option to `ember test` and `ember test
--server`. The `filter` parameter is used by QUnit to filter based on
module name and test description.
Merge pull request #2223 from linstula/allow-filtering-tests

Allow filtering tests run through testem.
Merge pull request #2219 from joostdevries/error-if-config-meta-missing

Give clear error when failing to read config from meta
update broccoli
Merge pull request #2224 from csantero/update-broccoli

update broccoli
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`