* lumiera_interface are now static structures, never wrritten
* introduced a lumiera_interfacenode which manages the dynamic data
of interfaces. The interfaceregistry now holds this nodes.
When interfaces cross depend on each other nested acquiring from
their acquire handlers would introduce cyclic references which cant
be cleaned easily. By flagging such nested acquisitions as weak the
respective handler functions can account for this.
Example: maintain 2 ref counters one for strong and one for weak
acquisitions. At release time all acquired nested handles get closed when
the strong counter drops to zero, which causes that cross reference
releases will eventually drop the weak count to zero too. Then all
resources can be freed and the interface is properly shut down.
Provides structures used for managing interfaces, macros for declaring
and defining interfaces. Convinience macros to bundle buildin and plugin
interfaces.
