- introduce basic define-typed-syntax instead of define-syntax
- add fomega3 --- same as fomega2, without the duplication
- app and lam are both types and terms
- arrow is both type and kind
- same tests as fomega2
- 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
- fomega2 is the same as fomega.rkt, except tyapp, tylam, and => are removed
- instead, #%app, \lam, and -> serve dual purpose at both term and type level
