Added functions for detecting known folders per-platform. Not tested on Windows yet, but who cares?

source/mijin/platform/folders.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#if !defined(MIJIN_PLATFORM_FOLDERS_HPP_INCLUDED)
+#define MIJIN_PLATFORM_FOLDERS_HPP_INCLUDED 1
+
+#include "../internal/common.hpp"
+
+#include <filesystem>
+
+namespace fs = std::filesystem;
+
+namespace mijin
+{
+enum class KnownFolder
+{
+    USER_HOME,
+    TEMP,
+    CACHE_ROOT,
+    USER_CONFIG_ROOT,
+    USER_DATA_ROOT
+};
+
+[[nodiscard]]
+fs::path getKnownFolder(KnownFolder folder) MIJIN_NOEXCEPT;
+}
+
+#endif // defined(MIJIN_PLATFORM_FOLDERS_HPP_INCLUDED)