Text wrap in Haskell code

This adds two functions in Utils.hs: 'wrap' and 'trim' along with some
simple tests. 'wrap' is used in Common.hs for wrapping command
descriptions to a fixed line length, e.g. useful for the "--help"
option.

Signed-off-by: Yiannis Tsiouris <gtsiour@softlab.ntua.gr>
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>