Allow belongs to associations to be saved when the associated object is null.
Remove accidentally added capitalize and camelize
[FIX] typeof null actually === 'object'

Fixed an issue where calling `isValue` with null would throw a
`TypeError` (Cannot read property then of null)
[Bugfix] embedded records mixin: key variable needed to be declared
Favour declared mapping over keyForAttribute, if defined;

keyForAttribute, if defined, is useful for defining custom changes for all keys on a particular serializer, be it for the application or just a particular resource. The custom attr-based mapping should be maintained, and should precedence, over the keyForAttribute.

Broke down the ternary operators for increased readability.

Adds integration test for mapping > `keyForAttribute` precedence
Allow `attr` mapping in `belongsTo` & `hasMany` attributes;

Related attributes should still be able to have mappings defined for them. The normalizing compliment to these mappings, `JSONSerializer#normalizeUsingDeclaredMapping`, are applied to all attributes including `belongsTo` and `hasMany`.

Adds integration test for mapping > `keyForRelationship` precedence;
Add guard before deleting partial[attribute]
Expected closing tag for payload._embedded.comment.forEach used in api docs
http://emberjs.com/api/data/classes/DS.RESTSerializer.html

Signed-off-by: Norik Davtian <norik@bigemployee.com>
Merge pull request #2086 from NorikDavtian/master

Expected closing tag for payload._embedded.comment.forEach used in api d...
Fixed grammatical issue on DS.PromiseObject page
Merge pull request #2087 from brendanwb/fix-promises-obj-typo

Fixed grammatical issue on DS.PromiseObject page
Merge pull request #2078 from f3ndot/serialize-using-declared-mapping

[BUGFIX] Use declared mapping during serialization, even if keyForAttribute or keyForRelationship are defined
Merge pull request #2081 from alexBaizeau/bug/identicalAttributeAndKey

Add guard before deleting partial[attribute]
Merge pull request #2061 from pixelhandler/fixup-embedded-records-key-variable-in-serialize-methods

[Bugfix] embedded records mixin: key variable needed to be declared
drop server responses if they are no longer relevant
Merge pull request #2067 from jcollins1991/drop_late_responses

Drop late responses
PERF: O(n) -> O(1) record within recordArray check

If a record changes, we attempt to re-add it to the array, addRecord only adds unique records to the array but does so with an O(n) indexOf. A proper solution would be for addRecord to utilize an index, unfortunately it does not (yet). Luckily we already have just such an index, that records recordArrays map.
Merge pull request #2090 from emberjs/reduce-cost-of-record-updates

PERF: O(n) -> O(1) record within recordArray check
Update Bower publishing to use correct username.
Refactored EmbeddedRecordsMixin to push records instead of sideload

Previously EmbeddedRecordsMixin just moved records around and relied on sideloading for their extraction. Now they are pushed to the store as they are parsed.

Benefits include:
1. Less confusing code
2. Out of the box sideloading support
3. Support for using EmbeddedRecordsMixin with JSONSerializer