It would be useful to be able to cast env variables to a specific type, for example: ```python def setup_config(config: Configuration): config.foo.from_env("VAR_FOO", cast=int, default=1) config.bar.from_env("VAR_BAR", cast=bool, default=True) ``` Inspired by https://www.starlette.io/config/ and https://github.com/sloria/environs