Deprecate unnecessarily partial functions

[josephcsible]

We should deprecate replace and splitOn, and create alternatives for them that take a NonEmpty instead of crashing at runtime when their first parameter is empty.

[ndmitchell]

While it is would be nice if they were pure, syntactically writing a NonEmpty, especially for a String is cumbersome - often the first arg is a constant. Perhaps safe variants should go in the List.NonEmpty.Extra, then people can pick their poison.