[Bugfix] Decouple DS.EmbeddedRecordsMixin from DS.ActiveModelSerializer

[Fixes #1974]
Fix class name in debugging message

`RestAdapter` should be `RESTAdapter`.
Merge pull request #2019 from tricknotes/fix-class-name

Fix class name in debugging message
Fixed a loose semicolon

Semicolon was unnecessary and causing a javascript error.
Merge pull request #2022 from rmartinez93/master

Fixed a loose semicolon
updated '_links' to just 'links'
Merge pull request #2024 from dadamssg/master

updated '_links' to just 'links'
fix documentation of `getById`
Merge pull request #2025 from Crunch09/master

fix documentation of `getById`
Merge pull request #1987 from pixelhandler/keyForAttribute-optional

[Bugfix] Decouple EmbeddedRecordsMixin from ActiveModelSerializer
fix documentation of 'attr'
Merge pull request #2027 from JustAboutJeff/DOCS-fix-attr

fix documentation of 'attr'