Added Envelope to synthdeftools.
Added Envelope to synthdeftools.

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