Re-add FunTy (big patch)

With TypeInType Richard combined ForAllTy and FunTy, but that was often
awkward, and yielded little benefit becuase in practice the two were
always treated separately.  This patch re-introduces FunTy.  Specfically

* New type
    data TyVarBinder = TvBndr TyVar VisibilityFlag
  This /always/ has a TyVar it.  In many places that's just what
  what we want, so there are /lots/ of TyBinder -> TyVarBinder changes

* TyBinder still exists:
    data TyBinder = Named TyVarBinder | Anon Type

* data Type = ForAllTy TyVarBinder Type
            | FunTy Type Type
            |  ....

There are a LOT of knock-on changes, but they are all routine.

The Haddock submodule needs to be updated too

1 files changed, 0 insertions, 0 deletions

diff --git a/libraries/vector b/libraries/vector
-Subproject 224eccbac0125b7bd302f24063bbb473b2c2e1d
+Subproject 6c17dd6fadc5e7e3e09f7892380ce1339f296ef