component:

component:
- add ability ro register abstract classes. These can register as implementing
  some interfaces, but are by default not listed by implementations()
- add automatic interface-to-component __doc__ propagation, with the
  @interfacedoc method decorator

api:
- general idea: prepare for processor "pipes" high-level api
- move process() into IProcessor, make it a generic method
- add IProcessors methods that relate to buffersize, and input/output format
- add IDecoder.nframes()
- add IEffect, an interface for effect processors

tests:
- fix testnewcore.py
- add test and examples of processors implementing the new api and component
  system

others:
- add empty Metadata class