Update CHANGELOG
Bump version
Add info on sending underscored JSON for create/update operations

In 0.13 the REST Adapter would send underscored JSON for create/update
requests.  Beginning in Beta 1 the REST Adapter sends camelized JSON.

This PR updates TRANSISTION.md to show how to get back to underscores.
Add assertion for non existing transforms
require the activemodel initializers
Fix bug in ActiveModelSerializer attempting to normalize polymorphic relationships even when they were not specified
Remove unnecessary variables
Return null from getById if the record isn't found
Merge pull request #1299 from jamiebikies/master

Return null from getById if the record isn't found
Merge pull request #1295 from stefanpenner/master

[fixes #1282] fixes the inflectors inflections /w irregular words
Merge pull request #1292 from dmathieu/activemodel_initializers

Require the initializer in the ActiveModel package
More thorough rollback
Only roll back in flight attributes if in error
Merge branch 'jeremy/underscore-json-serializer' of https://github.com/jagthedrummer/data into jagthedrummer-jeremy/underscore-json-serializer

Conflicts:
	TRANSITION.md
Merge pull request #1298 from markprzepiora/master

ActiveModelSerializer tried to normalize polymorphic relationships even when they were not specified
Clean up tests
Clean up unused helper functinos
Merge pull request #1310 from tricknotes/clean-up-unused

Clean up unused helper functinos
Stop extending if `String` flag is `false`

Allow `Ember.EXTEND_PROTOTYPES.String` is `false`.
Merge pull request #1319 from tricknotes/option-for-extending-string

Stop extending if `String` flag is `false`