Big refactor, shuffling a lot of files around

src/util/map_.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <map>
+
+namespace anm2ed::util::map
+{
+  template <typename T> int next_id_get(std::map<int, T>& map)
+  {
+    int id = 0;
+
+    for (auto& [key, value] : map)
+    {
+      if (key != id) break;
+      ++id;
+    }
+
+    return id;
+  }
+
+  template <typename T0, typename T1> T1* find(std::map<T0, T1>& map, T0 index)
+  {
+    return map.contains(index) ? &map[index] : nullptr;
+  }
+}