* [Haskell Servant] Upgrade to lts-12
- Upgrade Servant to the latest version
- Add Maybe for optional values
- Add UUID, UTCTime and Day types
- Fix the URL configuration so that it has one param with all data
- Add Data and ToSchema instances to models
- Switch to TLS http manager so it can connect to https urls
- Add nicer API to call the endpoints
- Add Nix support
* [Haskell Servant] Upgrade Petstore
* [Haskell Servant] Delete old swagger-petstore samples
* [Haskell Servant] Use generics for ToForm and FromForm instances
* [Haskell Servant] Generate ToSchema instance only if it's safe to do