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/CMakeLists.txt

@@ -192,6 +192,10 @@ set(SWA_INSTALL_CXX_SOURCES
 set(SWA_USER_CXX_SOURCES
     "user/achievement_data.cpp"
     "user/config.cpp"
+)
+
+set(SWA_MOD_CXX_SOURCES
+    "mod/mod_loader.cpp"
 )
 
 set(SWA_THIRDPARTY_SOURCES
@@ -251,7 +255,8 @@ set(SWA_CXX_SOURCES
     ${SWA_PATCHES_CXX_SOURCES}
     ${SWA_UI_CXX_SOURCES}
     ${SWA_INSTALL_CXX_SOURCES}
-    ${SWA_USER_CXX_SOURCES}
+    ${SWA_USER_CXX_SOURCES}
+    ${SWA_MOD_CXX_SOURCES}
     ${SWA_THIRDPARTY_SOURCES}
 )