Implemented constantly in functoolz

[caioaao]

Usage:

>>> f = constantly(42)
>>> f(any, parameters, here=80)
42

Examples in other languages:

• clojure's constantly
• haskell's const
• elm's always

[llllllllll]

This has already been discussed and rejected: #283

[caioaao]

Hm, didn't saw that, my bad. But still, I don't agree (see this stackoverflow answer).
Also, I'm coming back from clojure, and constantly is also somewhat redundant ((fn [& args] x) would have the same effect as (constantly x)), but adds readability to the code when used. In python, writting constantly(x) instead lambda *args, **kwargs: x makes the code clearer and smaller.
About not feeling it's a part of toolz: a function like this one is perfect for an API that makes heavy use of higher order functions.
PS: can't figure out why it's not passing CI tests 😓

[caioaao]

closing as it's stalled for over a year