Set operations such as in clojure.set that also works for vectors and keeps order, in a similar that it works for set.
Note: not a good support for lists yet.
Apart from the functions from clojure.set, this namespace have two extra functions:
* setish - returns a collection without duplicates
* restrict - same as select, but with xrel in fist position to play
well with (-> ...)
* update
* index-unique