Merge pull request #4296 from rjackson/doc-html5-attributes

[DOC beta] Document HTML5 attributes available.
[FEATURE ember-routing-inherits-parent-model] Route inherits parent's model by default.
Merge pull request #4246 from locks/model-inheritance

Route inherits parent's model by default.
[FEATURE ember-routing-consistent-resources]

Adds `.index`, `.loading`, and `.error` sub-routes for resources created
even if no callback was provided.

For example:

```javascript
  App.Router.map(function() {
    this.resource("home");
  });
```

Prior to this feature `home.index` route would not be created for the above resource.