add 'heights-interpolation', 'biomes-interpolation'

src/maths/Heightmap.hpp

@@ -2,6 +2,7 @@
 
 #include <vector>
 #include <string>
+#include <optional>
 
 #include "typedefs.hpp"
 #include "maths/Heightmap.hpp"
@@ -12,6 +13,8 @@ enum class InterpolationType {
     CUBIC,
 };
 
+std::optional<InterpolationType> InterpolationType_from(std::string_view str);
+
 class Heightmap {
     std::vector<float> buffer;
     uint width, height;