[Feature Request] Set `lisp` option

[alexmozaidze]

Some plugins use set lisp? to determine if the file is Lisp or not. It would be cool if you had lisp option set just so that outside plugins may detect Clojure as Lisp. It's possible for outside plugins to hardcode Clojure as Lisp, but I don't think that's the best approach.

[axvr]

Thanks for the suggestion. This will be included once #31 is merged into the master branch.