Class BuildInfo_CLibrary_External

Marshallable --+    
               |    
BuildInformation --+
                   |
                  BuildInfo_CLibrary_External

Return marshalling data for my attributes.

To be implemented by derived classes.

The returned marshalling data is a dictionary object that
contains relatively anonymous data which represents the object
to be marshalled. The dictionary is composed by derived
classes and must look as follows:

::

   {
      'generating_class': <class object of generating object>,
      'versions': <versions of contributions>,
      'attributes': <dictionary with direct attributes key/value pairs>,
   }

Called indirectly by `__getstate__`.

(To be documented)

Unique key to easily determine object equivalence. Used to
index BuildInformation objects, and to eventually sort out
duplicates.