Add toNev combinator in NonEmptyList

[saraiva132]

I wanted to get an instance of NonEmptyVector from a NonEmptyList and I noticed it was lacking that combinator.

Something like:

def toNev[B >: A](implicit order: Order[B]): NonEmptyVector[B] = 
    NonEmptyVector.fromVectorUnsafe(toList.toVector)

There might be more combinators missing.

[saraiva132]

I can pick this up, I will scavenge a bit to see what else is missing