A hacky way of checking if the current call to `method_missing` updates `@last`, used in [line #73](https://github.com/meh/paggio/pull/2/files#diff-582e934a5dd70ac68311ae953d47c922R73).

I've moved adding `@last` to `@class_names` out of this branch, so any classes set through attributes come before the class being set by this `method_missing`. This supports the rather awkward edge case `element.prefix(class: :other)[:suffix]`, demonstrated in [this test](https://github.com/meh/paggio/pull/2/files#diff-5ab6ee3ca0720222d553828929cdd1ecR140). Intuitively, if `element.prefix[:suffix]` creates a class `"prefix-suffix"`, we'd expect the same behaviour if adding other classes through attributes.

Only this branch knows if we're adding a new `method_missing`-style class name, though. `@last` could already be set and `name` always will be, so I'm using `prefix` here as a way of determining if I need to push it to the end of the `class_names` stack later, so it can be used as a class prefix with the `Element#[]`. Hence,

```ruby
@class_names.push(@last) if prefix
```

Probably going to revisit this when I take the case statement out though.