Style clean-up and small refactors

Hi there,

This is mostly a cosmetic PR and small refactoring to clean up styles according to the [Ruby Style Guide](https://github.com/bbatsov/ruby-style-guide). I find this much easier to read that what Hound suggests (single quoted strings, for example). Feedback welcome.
Ah, didn't mean to sneak this one in. That said, `Struct` is very handy when dealing with classes that do one thing and just require some initialization. Def doesn't make sense here, will fix.