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
pushing null should `end` the writeStream.