- do not use plain JSON rep for errors and use polymorphic variants instead
- split formatting for human readable and JSON output
- no more simple_errors simple_fails
- much less result bindings used in stages
* Ast_typed stage is now aware of the main function name
* main function type is checked against expected contract types
* Tezos.self (returning contract type) is checked against main function type
* In general, Ast_typed.compile signature has been changed to enable/disable contract-related checks
