encoder-stream: add EncoderStream class

When you call Encoder#stream(), one of these is what's going to be returned.
encoder: incorporate the EncoderStream class

Not quite working the way it should yet...
make `node_ogg_page_to_buffer()` synchronous
remove old `stream.js` file

Was getting way too big... now separated into EncoderStream and DecoderStream
classes.
don't export the OggStream class

Since it has been deleted...
test: remove old "stream.js" tests
encoder: finish up stream2 refactor for Encoder