add _debugInfo to Ep.Model

useful for debugging tools such as the Chrome Ember Extension
Merge pull request #50 from jasonkriss/debug

add _debugInfo to Ep.Model
Models with missing embedded keys can now be loaded
Modified previous patch to match the comment on it
Merge pull request #63 from ginty/missing_embedded

Models with missing embedded keys can now be loaded
Clarified the meaning of update

parent.update sounds like the action that's taken by the persistence layer to persist this model. In reality, it just refers to copying values from current model into parent session's corresponding model.
Merge pull request #69 from taras/patch-3

Clarified the meaning of update
remove .map file from source gem