[FEATURE ember-handlebars-log-primitives] Remove flags.
[FEATURE ember-testing-routing-helpers] Remove feature flags.
[FEATURE ember-testing-triggerEvent-helper] Remove feature flags.
[DOC] Add docs for MutableArray addObject and removeObject

* Add docs for addObject & remove Object, closes #4618
* Clean up code style and various docs on MutableArray
* Update old observer syntax example
Merge pull request #4624 from mixonic/doc-add-remove-object

[DOC] Doc add remove object
[FEATURE computed-read-only] Remove feature flags.
[FEATURE ember-metal-is-blank] Remove feature flags.
[FEATURE ember-eager-url-update] Remove feature flags.
[FEATURE ember-routing-auto-location] Remove feature flags.
[FEATURE ember-routing-bound-action-name] Remove feature flags.
[FEATURE ember-routing-inherits-parent-model] Remove feature flags.
Merge pull request #4623 from rjackson/remove-released-flags

Remove feature flags for 1.5.0 enabled features.
Add count to array computed meta