Add special case for g-object-ref-sink

Map the return type to <C-void*> to avoid an infinite loop in gobject-glue's
make method.
Generate object properties in a separate module

This resolves the problem of properties with the same name in different
modules, the users can choose how to handle this.
Merge pull request #37 from fracek/g-object-ref-sink-hack

G object ref sink hack + properties in separate module