Support encoding changing

I've used the great [`iconv-lite`](https://github.com/ashtuchkin/iconv-lite) library for recoding the read and written file content. This pull request should close #35 and open a way for implementing non-default encoding support in Atom.
`iconv.encode` returns a `Buffer` always right?

I don't think you need the `encoding: null` to `fs.writeFileSync` when called with a `Buffer`.