Mod loader implementation. (#66)

* Initial mod loader implementation.

* Allow iterating in mod directories.

* Initial append archive implementation.

* Avoid calling function wrappers when loading append ARs.

For some reason they cause issues. Should investigate later.

* UMM merge archive support.

* Load merge archives without archive lists.

* Less thread locals.

I shouldn't worry about string allocations this much when the game itself spams them...

* Check for read-only UMM archives.

TODO: Skip merging as it's currently just doing duplicate loads.

* Skip loading merge archives if they are read-only.

* Merge only archives.

* Implement decompression.

* Fix append ARLs not loading.

* Initial save file redirection implementation.

* Slightly refactor resolved path usage.

* Implement save file redirection fallback.

* Set a default save file path if none is provided.

* Check for enabled option & replace backward slashes with forward ones in mod save file paths.

* Convert back slashes to forward ones when iterating directories.

* Make CSB limit dynamic.

* Cache append/merge archive lookups.

* Close stream after reading compressed ARL.

* Fix UMM/HMM ARL file path inconsistency.

UnleashedRecomp/mod/mod_loader.h

@@ -0,0 +1,12 @@
+#pragma once
+
+struct ModLoader
+{
+    static inline std::filesystem::path s_saveFilePath;
+    
+    static std::filesystem::path ResolvePath(std::string_view path);
+
+    static std::vector<std::filesystem::path>* GetIncludeDirectories(size_t modIndex);
+
+    static void Init();
+};