build: add EnTT library

include/entt/container/fwd.hpp

@@ -0,0 +1,38 @@
+#ifndef ENTT_CONTAINER_FWD_HPP
+#define ENTT_CONTAINER_FWD_HPP
+
+#include "../stl/functional.hpp"
+#include "../stl/memory.hpp"
+#include "../stl/utility.hpp"
+#include "../stl/vector.hpp"
+
+namespace entt {
+
+template<
+    typename Key,
+    typename Type,
+    typename = stl::hash<Key>,
+    typename = stl::equal_to<>,
+    typename = stl::allocator<stl::pair<const Key, Type>>>
+class dense_map;
+
+template<
+    typename Type,
+    typename = stl::hash<Type>,
+    typename = stl::equal_to<>,
+    typename = stl::allocator<Type>>
+class dense_set;
+
+template<typename...>
+class basic_table;
+
+/**
+ * @brief Alias declaration for the most common use case.
+ * @tparam Type Element types.
+ */
+template<typename... Type>
+using table = basic_table<stl::vector<Type>...>;
+
+} // namespace entt
+
+#endif