bench: Add flag to be silent in runner

This is helpful in tracking down bailouts and deopts in Stream classes,
without triggering one from the string write in console.log
stream: Split Writable logic into small functions

1. Get rid of unnecessary 'finishing' flag
2. Dont check both ending and ended. Extraneous.

Also: Remove extraneous 'finishing' flag, and don't check both 'ending'
and 'ended', since checking just 'ending' is sufficient.
stream: Remove output function from _transform

Just use stream.push(outputChunk) instead.
stream: _write takes an encoding argument

This vastly reduces the overhead of decodeStrings:false streams,
such as net and http.
stream: Use class for write buffer entries
build: define nightly tag external to build system