v0.2.0

• Adds panner effect (PR #3 by @kristianj)
• Adds convolver effect (PR #4 by @JohnPaulHarold)
• Adds reverb effect (PR #5 by @JohnPaulHarold)
• Adds ping-pong delay effect (PR #6 by @JohnPaulHarold)
• Adds parameters when and offset in Sound objects