[ new ] add Data.List.grouped function

[stefan-hoeck]

Description

This adds a new function to Data.List for grouping a list into equal sized sub lists. For instance, group 3 [1..10] will return [[1,2,3],[4,5,6],[7,8,9],[10]]. I took the function's name from a similar function in Scala (see here).

The implementation is tail-recursive and runs in O(n).

Should this change go in the CHANGELOG?

• If this is a fix, user-facing change, a compiler change, or a new paper
  implementation, I have updated CHANGELOG.md (and potentially also
  CONTRIBUTORS.md).