Support keyword arguments in `s/defn`

```clojure
(s/defn foo [& {:keys [bar]}])
Bad & binding form: currently only bare symbols and vectors supported
```

Note that `clojure.core/defn` was recently enhanced to be able to provide a map in this case.

```clojure
(defn bar [& {:keys [bar]}])
(bar {:bar true})
```