Add initsNE, tailsNE :: Text -> NonEmpty Text

[Bodigrim]

Let's follow the suite of bytestring, which provides initsNE :: ByteString -> NonEmpty ByteString and tailsNE :: ByteString -> NonEmpty ByteString.

This would improve consistency between bytestring and text and dovetail nicely in the efforts to eliminate Prelude.head / Prelude.tail, allowing to use Data.List.NonEmpty.head in more situations.

For the reference, here is a relevant PR for bytestring: haskell/bytestring#557

CC @kindaro.

[kindaro]

On it!