introduced field_attributes shortcuts and added method on_base() to all processor classes

include/matador/object/primary_key_resolver.hpp

@@ -43,6 +43,8 @@ public:
     return resolver.resolve(obj);
   }
 
+  template<typename BaseType>
+  static void on_base(const BaseType&) {}
   template < class Type >
   void on_primary_key(const char *id, Type &pk, const utils::primary_key_attribute& attr) {
     primary_key_info_.pk_column_name = id;