Porposition for Issues 176 - coerce collections

this may be a solution to [this issue](https://github.com/intridea/hashie/issues/176#issuecomment-47101678)

I've update the readme, let me know how you guys like it.
Sorry to be a pest, there're two spaces after `,`. I'll fix this manually later on merge, but I'd appreciate if you amended before me. Thx.