A serializer implements `extractEmbeddedData` to retrieve embedded
associations data
Check against `null` and `undefined`
continue ember-dev cycle fixes, and also bump ember-dev
Rename none/empty to isNone/isEmpty variables

Rename none ti isNone and empty to isEmpty variables. It makes the code
easier to read.
Merge pull request #981 from karlguillotte/master

Rename variables none/empty to isNone/isEmpty
Ignore 'docs/node_modules'

`yuidoc` is installed into this directory.
Avoid incorrect tag warning

```
warn: (docparser): replacing incorrect tag: returns with return:
```

I rewrite `returns` -> `return`.
Merge pull request #985 from tricknotes/avoid-incorrect-tag-warning

Avoid incorrect tag warning
Merge pull request #984 from tricknotes/ignore-node-modules

Ignore 'docs/node_modules'
Simplify not-null-or-undefined check
Merge pull request #988 from joliss/null-checks

Simplify not-null-or-undefined check
Remove deprecated metaPath reliance

Ember.metaPath is no longer used anywhere in Ember and
will almost certainly be deprecated in this PR

https://github.com/emberjs/ember.js/pull/2710
Merge pull request #989 from machty/remove-meta-path

Remove deprecated metaPath reliance
Fix revision number in README.md

The guides seems to be described as revision 12.
bump ember-source
Remove findByClientId() test sync
Records are now looked up via recordForReference()
Merge pull request #991 from tricknotes/fix-revision-in-readme

Fix revision number in README.md
Merge pull request #990 from tricknotes/bump-ember-source

bump ember-source
Merge pull request #993 from rupurt/remove-unused-test-stub

Remove findByClientId() test sync
Document DS.Model create/_create