Fix pretty-printing bug in HsSyn
Check arity of type family instances.
Introduce CoVarId as a new IdDetails.
Fix testsuite output wibble.
Implement bidirectional type checking for types.
Add "dependent" tests
Hackily parse '*'.
Another test case.
Add another test; fix CoVarId detection.
Note about TH update.
Start rejigging rejigConRes
Make rejigConRes work, I think.

This makes rejigConRes aware of kind-indexed GADTs.
Change kind-coercion roles to be *representational*.
Fix kind coercion roles, for good. (I think).
Split UnivCo into PhantomCo and UnsafeCo.

Phantom coercions still need representationally-equal kinds.
Unsafe coercions do not. Oi.
Add TcCoherenceCo. But I think it's inadequately expressive.
When skolemising dependent coercions, treat them as givens.
Classify ~# as a pred type, so that the solver can think about it.
Extra logging in TcCan. Probably should revert.