Add new way of observing, using strings and new callback types
Use auto tracking of observers
Add HSSCascader visitor and use it
Add HSSLayout visitor and use it
Move HSSDirectionValue enum into HSSTypeEnums.h
Remove the toMap code from HSSObject
Remove old way of handling properties on hss objects
Let HSSObject handle the shorthand list when copying
Standardize on _initialize as method name for initialization
Add new infrastructure for hss objects' properties
Add properties using the new infrastructure
Fix typo
Remove superfluous content text functions from HSSDisplayObject and HSSContainer
Adjust const-ness
Enhance HSSValue so that it can work as a proxy object for constants
Improve the VisitorFilterFlags to make them more useful for layout
Code cleaning
HSSContainer: make appendContentText not virtual
Add beginning of dot notation
Set the shorthand list on HSSMargin