Move `err` declaration to function signature.
Scrap unnecessary `RunnerPlugin` pattern for FileOutput (i.e. no more FileWriter) and
integrate batch support directly into the output plugin. First step toward an abstracted
batch output pattern that can also be used by other outputs.
Use []byte for the batch buffers instead of *[]byte.
Forgot to actually start the output. Added the waitgroup support for good measure.
Need to add to the ref count to ensure our pack doesn't get zeroed before we're done.
Merge pull request #39 from mozilla-services/features/fileoutput-reboot

Features/fileoutput reboot