add 'meta' option to emit metadata in stream

This is a great module! Thanks for making it.

One thing that tripped me when I was getting started with this module is that it emits the file's metadata into the stream. I think this is the wrong default behavior because it violates the 'principle of least astonishment'.

This PR turns off this behavior by default, and adds a `meta` option to re-enable it.

What do you think?

(Depends on PR #4)