Add Web and Window streams

Adds WebStream and WindowStream.

WebStream is a promise stream decorator for WebSocket, WebWorker, and
MessagePort.  This is factored out of Q-Connection, which should be
factored to take advantage.

WindowStream provides facilities for handshaking between windows and
iframes, to produce promise streams.

What was Buffer is now BufferStream, which replaces the old buffer
stream even though the interface is incompatible.

Thus, theses changes will need to be released in a major release.