Improve Haddock markup

This fixes the markup at the top of `Control.Arrow`, and improves the
markup inside DEPRECATED strings.

(Haddock supports markup inside DEPRECATED messages, which allows to
turn references to Haskell entities into hyperlinks by using the usual
Haddock markup.)

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
Derive `FiniteBits` for integral newtype wrappers

When `FiniteBits` was introduced in cddc9024e67a6d4c01bb190839d0134af8c907e0
only the standard Haskell 2010 finite-size integral types were given a
`FiniteBits` instance, however, since also a DEPRECATION warning was put
in place (as per 701d9ed4b2bec5922709a91bfb625881d7dd47f0) for `bitSize`
which might point people to to `FiniteBits`, it seems sensible to derive
`FiniteBits` for all integral newtype wrappers as well.

N.B.: This makes `Integer` the only type in `base` with a `Bits`
      instance but no `FiniteBits` instance.

Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>