Update core spec to reflect changes to Core
Update core spec to reflect changes to Core. Key changes: * Adds a new rule for forall-coercions over coercion variables, which was implemented but conspicuously missing from the spec. * Adds treatment for FunCo. * Improves commentary (including restoring a Note lost in 03d4852658e1b7407abb4da84b1b03bfa6f6db3b) in the source. No changes to running code.
Would like review from @simonpj.