Codegen io-ts for open api schema

[baetheus]

There is a json schema for openapi 3.0. There are also schemas for swagger 2.0. A good project would be to revisit schema.ts and generalize it for a fuller featured json schema (likely only need to add a semigroup to handle refs to clean up the ref naming). Then we could generate the openapi parser from the schema instead of maintaining it by hand.