Make the main dupli instance creator function public so it can be used
from RNA.

The function takes a dupli result argument, which makes it quite safe
and reduces possibility of error by ensuring it can only be used during
the duplicator execution.
RNA representation of the DupliResult struct.
Registerable make_duplis function in the duplicator RNA struct.
Added a new dupli type and RNA enum wrapper for custom dupli types in
objects.