- make all parameteres consistently singular
- rename `settings` to `config`
- rename `env_type` to `var_type`
- rename `environment` (in input/output, settings) to `environment_var`
- rename `inputs` to `input` and `outputs` to `output`; and enable single value OR list
- add `optional` to input/output
- add `[<SERVICE_DEFINITION>]` to chain so that it can define its own compose service
- add `<FURTHER_COMPOSE_DEFINITION>` to chain and code velds