- fixes fomega bug where kind annotations were not being compared
- fix subst bug: must tranfer props (ie types) when replacing an id
- add exist tests to check proper subst in ty=
- previously forgot to add stlc+rec-iso.rkt and tests
- rename files with records (eg stlc+var, stlc+rec+sub)
- use "reco" to avoid confusion with recursive types ("rec")
- start exist.rkt --- existential types