Pointer cleanup (#242)

- Made greater use of smart pointers, eliminating many instances of manual memory management
- Do not use pointers at all for many non-polymorphic classes
- Assorted other code cleanup

model/ParserState.h

@@ -47,7 +47,7 @@ namespace glabels
 
 
 		private:
-			const QString* mString;
+			const QString* mString{ nullptr };
 			qsizetype      mPos{ 0 };
 		};