Clojurians Log v2

I'm thinking of using the same logic as get but refine the return value based on the knowledge that the entry exists. As opposed to disallowing maps that don't have the key, i.e.,

(req! {:a 1} :b) ;; type checks

especially useful for this case:

(fn [m :- (Map Str Str)] (req! m "a"))

we can infer Str return in that case.