* ASTraitCollection now completely reflects UITraitCollection

* Add ASContentSizeCategory enum that corresponds to
  UIContentSizeCategory and can be used inside a struct.

* Use __unsafe_unretained UIContentSizeCategory instead of the enum.

… ASTraitCollection-missing-properties

# Conflicts:
#	CHANGELOG.md
#	Source/Details/ASTraitCollection.m

* Restore one of the ASTraitCollection constructors with a deprecation notice.
* Clean up API by the separation of tvOS-specific interfaces.
* Use [NSString -isEqualToString:] for ASPrimitiveContentSizeCategory equality tests for better readability.
* Encapsulate fallback logic for UIContentSizeCategoryUnspecified.