Honestly I don't even know what arity means anymore :/ It isn't even included in the ruby definition.

```
irb(main):001:0> def x(a, b, c:); end
=> :x
irb(main):006:0> method(:x).arity
=> 2
```

Though ruby arity has never really made sense (i.e. negative values for splatted arguments). Maybe as part of renaming this class just use a different word ... but what?

Max arity in this context is "if I represent my arguments as an array, what is the maximum length of that array?"

Also that TODO is no longer relevant, I need to remove it.