Merge pull request #87 from drogus/get-attr

Add getAttr hook
Only findMany ids which aren't in the identity map
Merge pull request #88 from darthdeus/smart-find-coalescing

Only findMany ids which aren't in the identity map
Fix findMany not resolving for only cached ids
Merge pull request #91 from darthdeus/fix-find-many-promise

Fix findMany not resolving for only cached ids
Improve Ember.hasMany

* make it non-embedded by default
* allow to pass options (options['key'] specifies key for the
  association)
* use references instead of ids in HasManyArray, this allows adding
  records without an id to HasManyArray
Implement basic version of belongsTo
Add getBelongsTo and getHasMany hooks