Add metadata to suggestions

[danielcompton]

Kibit makes suggestions that are valid most of the time but are not always exactly equivalent. #83 is a good example of this, where into [] and vec behave differently when used with core.reducers. I think it would be useful to be able to add comments to rules to explain these caveats.

There are also new Clojure forms that were introduced in 1.6. It would be good to check the version of Clojure the project is running on and only present rules that are valid on their version of Clojure.

[yogsototh]

Also, (not (empty? x)) is not always equivalent to (seq x) (the same for (when-not (empty? x) ...) )