Parse fireplant XML tag
Parse star XML tag
Parse moon XML tag
Add function for testing the new XML loader (not used yet)
Add warning for possible sync problems in Create_Level_Objects_From_XML_Tag()
Add CMake option to try the new XML loader.

In order to use the new level XML loader, you have to enable a compile-time
option like this when configuring the build:

  $ cmake -DENABLE_NEW_LOADER=true <other options> ..

Note that at the current state the new loader does not support savegames
yet (they will be loaded using the old loader). This will be added later.