Expose buffer

[tjconcept]

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.

[dominictarr]

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.