make goldpile subclass feature

src/goldpile.cpp

 #include "include/goldpile.h"
 #include "include/coord.h"
+#include "include/feature.h"
 
 GoldPile::GoldPile(Coord pos, int amount)
-	: position(pos)
+	: Feature('*', pos)
 	, amount(amount)
-	{}
-
-Coord GoldPile::getPosition() {
-	return position;
-}
+{}
 
 int GoldPile::getAmount() {
 	return amount;

src/include/goldpile.h

 #include "coord.h"
+#include "feature.h"
 
 #ifndef GOLDPILE_H
 #define GOLDPILE_H
 
-class GoldPile {
+class GoldPile : public Feature {
 	public:
 		GoldPile(Coord, int);
-		Coord getPosition();
 		int getAmount();
 	private:
-		Coord position;
 		int amount;
 };