Pipelet class methods add(), set_default_options(), build(), and Compose():
  - add( name, pipelet ):
      Add a pipelet method to the Pipelet base class.

  - set_default_options( source, parameters ):
      Set default options for pipelet parameters.

  - build(): debug and use for 'set' pipelet

  - Compose( name, composition [, context / constructor] ):
      allows to Compose a pipelet from other pipelets.