Guidelines for binary stream-likes should be added

[cynthia]

Related to w3ctag/design-reviews#92.

There are a bunch of new specs that deal with binary stream-like interfaces, which are not very well unified. We should add a section about this.

[travisleithead]

(Transposing my comment from #86 here)

Moving w3ctag/design-reviews#92 into this repo. This will be the primary entry point for the goals stated in the previous issue:

• Get the various streams straightened out
• Understand the use cases
• Write it all down (or at least the good parts) into our Design guidelines.

Relevant Meeting minutes:

• https://pad.w3ctag.org/p/30-10-2015-minutes.md
• https://pad.w3ctag.org/p/2016-07-30

We want to provide developers with a guide to when/how to use Streams (and what kind) in their designs.