Rubocop!

There's a new cop in town, and he's really picky about ruby syntax!

So `.rubocop_todo.yml` is a list of rules which haven't been dealt with yet.  Things moved into the `rubocop.yml` are things which either we think shouldn't be dealt with or things that we want to configure differently from rubocop's defaults.  Everything that I've moved from the todo is correctable by running `rubocop -a`, so that means it's really easy to fix them (so far)