"Safer" implementation of Data.List.NonEmpty (and some other suggestions)

Those implementations using the nontotal `fromList`seem inefficient and potentially dangerous. To eliminate those, I wrote a modification of the original file, which is enclosed. Some other suggestions: `insertBy` for `NonEmpty`s `NonEmpty [a]` to `[NonEmpty a]` transposition Add fixity for (:|) as `infixl 4 :|`