Multi-protocol

Lots of chagnes to add multi protocol flexibility, not really
completed yet, still have to rework text messages opcodes and other stuff,
so this still a working in progress feature

* Rework dat reader, the dat reader can now
* dinamically detect dat version
* Split game into gamelib and game_interface
* Lots of other minor changes

modules/corelib/util.lua

@@ -132,6 +132,7 @@ function getfsrcpath(depth)
 end
 
 function resolvepath(filePath, depth)
+  if not filePath then return nil end
   depth = depth or 1
   if filePath then
     if filePath:sub(0, 1) ~= '/' then