Allow belongs to associations to be saved when the associated object is null.
Remove accidentally added capitalize and camelize
Add failing test for hasMany relationships

If adapter does not return any data for a hasMany relationship,
the unsaved hasMany records disappear from the relationship.
Fixes #1466
Always keep the hasMany around when payload arrives

We should always keep the current hasMany value if the payload
has no relationships with that key
[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'
Added documentation for ajaxError with DS.Errors.
rest_adapter: Remove unused `set` definition
Merge pull request #2033 from duggiefresh/rest_adapter

rest_adapter: Remove unused `set` definition