In looking at Trac #9063 I decided to re-design the default
instances for associated type synonyms.  Previously it was all
jolly complicated, to support generality that no one wanted, and
was arguably undesirable.

Specifically

* The default instance for an associated type can have only
  type variables on the LHS.  (Not type patterns.)

* There can be at most one default instances declaration for
  each associated type.

To achieve this I had to do a surprisingly large amount of refactoring
of HsSyn, specifically to parameterise HsDecls.TyFamEqn over the type
of the LHS patterns.

That change in HsDecls has a (trivial) knock-on effect in Haddock, so
this commit does a submodule update too.

The net result is good though.  The code is simpler; the language
specification is simpler.  Happy days.

Trac #9263 and #9264 are thereby fixed as well.

This matches GCC's choice of Unicode quotation marks (i.e. U+2018 and U+2019)
and therefore looks more familiar on the console. This addresses #2507.

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