Only setting content-type to JSON if there actually is content.
Merge branch 'master' of github.com:enyo/data
Added a test for the content-type.
Failing test: 'When a record is loaded a second time, isLoaded should stay true'
Add docs directory with package.json and yuidoc.json

`EMBER_PATH=../ember-data rake preview` in ember-website does not quite
work yet. I don't have time at the moment to get it working completely,
but let's have the docs directory as a starting point.
Potential fix for #731
Use Ember.isNone for null check instead of !

Using !id to check for a null belongsTo id was causing relationships to be treated as missing.
Move createSerializedForm to DS.Serializer.  Serializer calls the routine currently, but it's only defined in the JSON and Fixture implementations.
Added 'isLoading' flag to DS.State
Add assertion for expected data hash when updating a record
Serialize id of belongsTo relationship via serializeId
Merge pull request #741 from pangratz/fix/serialize_ids

Serialize id of belongsTo relationship via serializeId
Merge pull request #766 from brigham/master

Make belongsTo recognize id 0
Rename none to isNone
Merge pull request #743 from CrowdStrike/yuidoc

Add docs directory with package.json and yuidoc.json
Merge pull request #731 from go1dfish/reload-isloaded

Failing test: 'When a record is loaded a second time, isLoaded should stay true
Switch serialized/deserialized argument names
Updated against master
Merge pull request #873 from JasonKriss/patch-1

Switch serialized/deserialized argument names
Merge pull request #815 from everwakeful/master

Extend existing "meta" solution for JSON REST responses