update region file format 2 to 3 (WIP)

src/files/compatibility.hpp

@@ -0,0 +1,14 @@
+#pragma once
+
+#include "typedefs.hpp"
+#include "util/Buffer.hpp"
+#include "files/world_regions_fwd.hpp"
+
+namespace compatibility {
+    /// @brief Convert region file from version 2 to 3
+    /// @see /doc/specs/region_file_spec.md
+    /// @param src region file source content
+    /// @return new region file content
+    util::Buffer<ubyte> convertRegion2to3(
+        const util::Buffer<ubyte>& src, RegionLayerIndex layer);
+}