To my big surprise, the cycle function from base is partial: it fails on empty lists

ghci> :t cycle
cycle :: [a] -> [a]
ghci> cycle []
*** Exception: Prelude.cycle: empty list

It's a bit problematic, since we don't want to expose partial functions. I see the following options:

1. Don't reexport cycle.
2. Change its type to NonEmpty a -> NonEmpty a.
3. Reimplement manually by returning empty list when empty list is given.

@vrom911, what do you think?