- Move mapping key from Protected to PNObject

Pod/Classes/PNObject.h

@@ -10,6 +10,14 @@
 #import "PNObjectConfig.h"
 #import "PNObjectModel.h"
 
+#pragma mark MappingSelector Keys
+
+extern NSString* _Nonnull const PNObjectMappingKey;
+extern NSString* _Nonnull const PNObjectMappingType;
+extern NSString* _Nonnull const PNObjectMappingSelector;
+
+#pragma mark -
+
 @protocol PNObjectSubclassing <NSObject>
 
 @required