setish

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