Implement shop purchase limits

src/main/java/emu/nebula/util/String2IntMap.java

@@ -0,0 +1,15 @@
+package emu.nebula.util;
+
+import it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap;
+
+public class String2IntMap extends Object2IntOpenHashMap<String> {
+    private static final long serialVersionUID = -7301945177198000055L;
+
+    public int get(String key) {
+        return super.getInt(key);
+    }
+
+    public FastEntrySet<String> entries() {
+        return super.object2IntEntrySet();
+    }
+}