Added luasnap checkpointing mechanism

luprex/cpp/viewer.hpp

@@ -16,9 +16,13 @@ public:
     Viewer();
     ~Viewer();
 
+    // Snapshot/rollback the lua state (temporary hack)
+    void snapshot() { world_->lua_snap_.snapshot(); }
+    void rollback() { world_->lua_snap_.rollback(); }
+    
     // Get the lua state for interaction.
     //
-    lua_State *get_lua_state() { return world_->get_lua_state(); }
+    lua_State *state() { return world_->state(); }
 
     // Get the player ID of the current player.
     //