Added UGen.outputs property, mirroring UGen.inputs.
Added UGen.outputs property, mirroring UGen.inputs.

josiah-wolf-oberholtzer/supriya,andrewyoung1991/supriya,Pulgama/supriya,andrewyoung1991/supriya,andrewyoung1991/supriya,Pulgama/supriya,Pulgama/supriya,Pulgama/supriya