Fix-bug : child primitive type didn't return parent's subtype list when it doesn't have any subType by itself. - isNaturalType checks rootBaseType. Therefore it will return empty array even if it doesn't have any subType and parent scheme has subType.
add new feature to support UTC timestamp in millisecond for Objective-C.
Merge pull request #6 from SanggeonPark/develop

Support UTC timestamp in millisecond.