[libredwg] iterator methods

[Felipe Sanches]

I have just git pushed a fix to our iterator routines.

These routines allow the application to loop through all owned objects of a group (BLOCK)

The functions are:

Dwg_Object* get_first_owned_object(Dwg_Object* hdr_obj, Dwg_Object_BLOCK_HEADER* hdr);
Dwg_Object* get_next_owned_object(Dwg_Object* hdr_obj, Dwg_Object* current, Dwg_Object_BLOCK_HEADER* hdr);

During the development of it I have noticed that we are storing version info in several places in our data structures. We should redesign it so that version of the DWG file being processed is stored in a single place.

-Felipe Sanches