Further separation of concerns between lib and bin?

[paulyoung]

Related to #5. Not entirely sure how far I want to go with this or if there's any real benefit.

Potentially the index file could return data and allow the binary to handle writing to disk.

[puzrin]

There are no real benefits to create bin folder for binary in such simple progect. Anyway, executable link is defined in package.json. I'd place it right in root - no needs to overcomplicate things.