Cleaned up the reflection code a bit

* Renamed 'tag' variable to 'handler'
* Removed addAlias stuff, instead check for matching names with if statements
* Added after_reading function that is called by Reader after reading a complete object. This generalizes Packaged::validate, which is now also called via this mechanism.
* Removed some backwards compatibility with <0.3.0 for templates

src/data/pack.hpp

@@ -56,6 +56,7 @@ class PackType : public IntrusivePtrBase<PackType> {
   private:
   DECLARE_REFLECTION();
 };
+void after_reading(PackType&, Version);
 
 /// An item in a PackType
 class PackItem : public IntrusivePtrBase<PackItem> {