Started to document serialization support
Extracted -transformedValue:ofPropertyDescription: and -reverseTransformedValue:ofPropertyDescription:

Cleaned serialization transformer related code to be fully symmetric.

Removed assertions related to serialization accessors in -valueForSerializedValue:ofType:univaluedPropertyDescription:, now useless due to -[ETPropertyDescription persistentType].
Fixed -reverseTransformedValue:ofPropertyDescription call time

This change ensures -reverseTransformedValue:ofPropertyDescription: is called in a way that is symmetric to -transformedValue:ofPropertyDescription:.

Note: this fixes test failures in EtoileUI test suite appearing with the previous commit.
Merge branch 'master' into serialization-rework
Fixed duplicated method implementation resulting from the merge

This was causing a test failure.
Made -serializedReferenceForObject: easier to read with a guard clause

Removed useless ETUUID/COPath case that never occurs in -serializedValueForValue:univaluedPropertyDescription:.
Removed special case to support serialization getters in -serializedTypeForUnivaluedPropertyDescription:ofValue:, we now leverage ETPropertyDescription.persistentType

Added -primitiveTypeFromValue: for persistent properties with a dynamic type (currently marked with NSObject).

Extracted -serializedTypeForNumber:.
Let persistent object graph contexts reference arbitrary inner objects in a transient object graph context (rather than just the root object)
Added -isLoading
Cleaned and explained a bit dynamic type case in -serializedTypeForUnivaluedPropertyDescription:ofValue:

Fixed missing return in the same method
Merge pull request #12 from etoile/serialization-rework

Merge latest progresses from Serialization rework