Add a flags parameter to all decoding functions for future needs

As of now, the parameter is unused, but may be needed in the future.
I'm adding it now so that in the future both API and ABI remain
backwards compatible as long as possible.

This is a backwards incompatible change.

doc/github_commits.c

@@ -117,7 +117,7 @@ int main(int argc, char *argv[])
     if(!text)
         return 1;
 
-    root = json_loads(text, &error);
+    root = json_loads(text, 0, &error);
     free(text);
 
     if(!root)