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pass options - Issue#109
Removing references from parents

Removing references from parents when changing relation
added a test case for removing references from parents  ( Issue #111 )
introduce a separate property to avoid confusion with set options - Issue #109
refactored _createCollection method - issue #109
modified comment to be more indicative...
also allow `collectionOptions` to be a function - issue #109
Check existence, not value of identity

In relations with type Backbone.One, _setAttr was checking that data's id
has a truthy value before comparing the identity with currVal's. This
means that if id's value is falsy, such as 0, the predicate fails even if
the actual values were the same. By checking for the id's existence
instead, we match things up correctly even with falsy identities.
Removing references from parents

Removing references from parents when using destroy [optional]
added a test case for removing references from parents ( Issue #113 )
Update CHANGELOG.md
remove unnecessary parameter...
refactor error handling and the transformation of raw collectionType/relatedModel to their final value
minor refactor of map transformation
comments and private method name changes
_proxyCallback can't be off
Test case ( Issue #115 )