Merge branch 'release/0.3.8' into develop
[update] deprecated description
[update] default datetime mapping timezone from Europe/London to UTC
Merge branch 'feature/datetime_mapping' into develop
[pod] Kiwi -> 2.3.0
[update] tests wrapper extension to xctest
[update] datetime specs
Merge branch 'feature/xcode_6_support' into develop
[update] global headers
[rename] for FEMAttributeMapping internals
[add] initial spec for FEMAttributeMapping
[add] shortcuts tests for AttributeMapping
[fix] AttributeMapping specs type
[add] spec for URL mapping NSNull check
[add] spec for date mapping NSNull check
resolve #18, resolve #19
Merge pull request #20 from Yalantis/feature/invalid_mapping

feature/invalid_mapping
[add] tests for missing relationships check
[add] handling of nil relationship data
[add] handling of missing relationship key for ObjectDeserializer
[update] null-relationship assignment
Merge pull request #21 from Yalantis/feature/null_relationship

Null relationship