Feature Request: Be able to cancel a Seq

[duysqubix]

Hello!

Beep has been fantastic to use. However I'm having some difficulty with the following situation.

I have a Seq of a StreamSeekCloser followed by a BeepCallback() to tell me when the audio file is done. Sometimes I'd like to stop streaming early, but If I close the StreamSeekCloser then my BeepCallback gets called.

I took a look at the implementation of Seq and it doesn't look like I can alter the items of the sequence after creation, which means I can't purposefully remove the BeepCallback() and then close the stream.

Would you be open to adding the ability to cancel a Seq which would cancel the current stream and then not run any of the other streams?

Thanks!

Original issue: faiface/beep#67

[MarkKremer]

Related: #16

[MarkKremer]

It's possible to put a Ctrl around the Seq and set its Streamer property to nil before you close the StreamSeekCloser. That way no samples will be consumed and the callback won't be called.