Proposal: Add singleton function to Data.List module

[Herbert Valerio Riedel]

> The point is to create a monomorphic variant [...]

But we already have at least two monomorphic variants to express this
with Haskell's concise native syntax and vocabulary which has by
design a preferential treatment of lists (it was considered even more
important than type-sigs so that we got the `:` cons operator for
lists and the `::` for type-sig annotations) -- so let's not try to
fight Haskell's core idioms by hiding them behind some trivial
additional redundant synonyms! I still fail to see the actual
*technical* problem being solved by the original proposal asking to
add yet another, wordy way to construct single-item-lists.