Alternative column size notation?

Currently `g/col` looks like:

``` clojure
(g/col {:xs 12 :sm 12 :md 12 :lg 12} "Some Text")
```

It would be nice to have an alternative (higher priority?) attributes, `:sizes`:

``` clojure
(g/col {:sizes [12 12 12 12]} "Some Text")
```

Even if all 4 sizes are required, it's still considerably more succinct.

Just a small thought I had while writing this out again and again!
