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

include/matador/sql/object_pk_binder.hpp

@@ -19,6 +19,8 @@ public:
         binder_ = nullptr;
     }
 
+    template<typename BaseType>
+    static void on_base(const BaseType&) {}
     template<typename ValueType>
     void on_primary_key(const char *id, ValueType &value, const utils::primary_key_attribute& attr);
     static void on_revision(const char * /*id*/, unsigned long long &/*rev*/) {}