Migrate to pipe. Dropped rotation options.

Fixes #28 

There are some things that may seem odd about this code, (`file` vs `directory` options) but there are plans to add the time rotation back in and I left some of the logic in there to make that easier.

- TODO add more validation on the options. https://github.com/hapijs/good-file/issues/33
Err, and since `writableStream` hasn't been unpiped from `readableStream`, you stand the chance of losing data or [triggering an error](https://github.com/joyent/node/blob/v0.10/lib/_stream_writable.js#L181).