added potion and restore_health

src/potion.cc

@@ -0,0 +1,12 @@
+#include "potion.h"
+
+potion::potion(const potion_type type, const int duration):
+        type{type}, remaining_duration{duration} {}
+
+potion_type potion::get_type() const {
+        return type;
+}
+
+int potion::get_duration() const {
+        return remaining_duration;
+}