Appends a
n character to each input string, then concatenates
the results. Equivalent to
foldMap (s -> s ++
"n").
>>> unlines ["Hello", "World", "!"]
"Hello\nWorld\n!\n"
Note
unlines . lines /= id when
the input is not
n-terminated:
>>> unlines . lines $ "foo\nbar"
"foo\nbar\n"