[#221] Add unsafe versions of "1" functions

Problem: sometimes user is completely sure that his structure is not
empty, he may want to use the original `foldr1` and `maximum` from
`Data.List`.

Solution: make those and similar functions be provided in `Unsafe`
module.

src/Universum/Unsafe.hs

@@ -22,9 +22,16 @@ module Universum.Unsafe
  , at
  , (!!)
  , fromJust
+ , foldr1
+ , foldl1
+ , minimum
+ , maximum
+ , minimumBy
+ , maximumBy
  ) where
 
-import Data.List (head, init, last, tail, (!!))
+import Data.List (foldl1, foldr1, head, init, last, maximum, maximumBy, minimum, minimumBy, tail,
+ (!!))
 import Data.Maybe (fromJust)
 
 import Universum.Base (Int)