Replace all free calls with VVV_free[func]

This replaces all calls to SDL_free with a new macro, VVV_free, that
nulls the pointer afterwards. This mitigates any use-after-frees and
also completely eliminates double-frees. The same is done for any
function to free specific objects such as SDL_FreeSurface, with the
VVV_freefunc macro.

No exceptions for any of these calls, even if the pointer is discarded
or zeroed afterwards anyway. Better safe than sorry.

This is a macro rather than a function that takes in a
pointer-to-pointer because such a function would have type issues that
require casting and that's just not safe.

Even though SDL_free and other SDL functions already check for NULL, the
macro has a NULL check for other functions that don't. For example,
FAudioVoice_DestroyVoice does not check for NULL.

FILESYSTEM_freeMemory has been axed in favor of VVV_free because it
functionally does the same thing except for `unsigned char*` only.

desktop_version/src/CustomLevels.cpp

@@ -9,6 +9,7 @@
 #include <tinyxml2.h>
 #include <utf8/unchecked.h>
 
+#include "Alloc.h"
 #include "Constants.h"
 #include "Editor.h"
 #include "Enums.h"
@@ -267,7 +268,7 @@ bool customlevelclass::getLevelMetaDataAndPlaytestArgs(const std::string& _path,
 
     std::string buf((char*) uMem);
 
-    FILESYSTEM_freeMemory(&uMem);
+    VVV_free(uMem);
 
     if (find_metadata(buf) == "")
     {