Add tests for calling jQuery.ajax from DS.RESTAdapter
Fix: unload record with relationships

- calling `clearRelationships` before changing record state,
  otherwise it fails, because properties try to update removed
  relationships

- Transaction commit failed when an unloaded record was in the
  `transaction.bucketForType.updated` array. Using recordIsMoving fixed
  this issue
fix test description
fixed issue #582
added adapter integration test for dirtyRecordsForAttributeChange
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.
Add live query test for RecordArray
Potential fix for #731
Add Ember.Date.parse to fix cross browser bugs parsing ISO-8601 dates
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.
Remove unused method

DS.Model#setProperty is no longer working.
Fix typo in addRelationships documentation
Do not allow setting to essentially read-only setters

If you set to any of the essentially read-only computed properties
such as: isLoaded, isReloading etc... on model, you are going to have
a really bad time.
Merge pull request #801 from stefanpenner/unsetableProperties

Do not allow setting to essentially read-only setters
Improve error message

`fixture` is an instance of `Object`.

Before:
```
the id property must be defined for fixture [Object object]
```

After:
```
the id property must be defined for fixture {"foo": "bar"}
```
Use `toString` if environment doesn't support `JSON.stringify`
Fix docs for Adapter's map API
Merge pull request #808 from JasonKriss/map-docs

Fix docs for Adapter's map API
Update to 'relationship' terminology