Expose buffer

In some situations it is useful to know what is in the buffer, how big it is, or even manipulate the data.
An example is streaming media. If the buffer reaches a threshold you'll want to wipe the buffer, decrease quality, and start filling it again.

sure - but really this module shouldn't be your go to. there is usually a more pull-stream way to do it, although I'd be happy to merge a PR that enabled more pully ways to use this.