Add worked-out writable stream examples. Closes #48.
Leftover "finished," should be "closed."
Explain that subclasses can override behavior.

That is, they don't have to use the internal buffer, but can instead use OS-level stuff, or their own things.

Closes #50.
Fix outdated API usage in Examples.md.
Be more explicit about return value from [[push]].

Fixes #54.
Add the beginning of a reference implementation.

Includes most of BaseReadableStream, with some tests, and skeleton tests for the rest.
Add missing return value to BaseWritableStream's close.

Thanks @othiym23!
Merge remote-tracking branch 'upstream/master'

Conflicts:
	reference-implementation/index.js
	reference-implementation/lib/base-readable.js
	reference-implementation/test/base-readable-stream.js
	reference-implementation/test/base-writable-stream.js