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

[박신환]

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 :|` 
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