New GDL Parser merged

[Arjen Hiemstra]

Hi people,

I have just pushed the new GDL parser work to master. This replaces the 
GDLHandler class with GDLSerializer which uses a generated parser internally. 
For the most part, this change is mostly a clean API change that requires less 
code. Please see core/gdlserializer.h for the new API.

There are some minor changes to the GDL language. Primarily, strings and 
references now need to be quoted. Certain things have been cleaned up as well 
though, for example, we can now use multiple root objects properly.

- Arjen