Create a dedicated section for interfacing with other specs

This incorporates much of https://fetch.spec.whatwg.org/commit-snapshots/ad9a84ad91fb6bd3a2dcdf0406321785f51c4c11/#streams, as well as https://wicg.github.io/compression/#generic-transform-stream. It also looks at how https://wicg.github.io/native-file-system/ uses writable streams, and creates wrapper algorithms to make that easier.

Closes #372.

Author: domenic