Add jpeg blob capture

[nijk]

Addresses issue #48

[spite]

So what does this return when .save() is called?

[nijk]

I guess I haven't really catered for the case where .save() is called without a callback - I suppose I haven't considered it because it doesn't really make sense to do that when you want to obtain an array of blobs rather than having the capturer download a collection of files for you.

On reflection, it may be a better pattern to augment the existing CCJPEGEncoder to allow the flexibility of a Tar of Images or Array of Blobs on .save() and also allow for the callback on each frame .add().

[nijk]

@spite Any thoughts on this?

[spite]

I guess I don't understand why you need to create a new Frame Encoder. Why doesn't the current JPEG/PNG encoder work for your needs?