[feature request] Single FOO_BAR_ARGS environment variable

IIUC one can add `env "PORT"` (and accompanying `subEnv "FOO_BAR_"`) to have environment variables support for arguments. Another nice environment variables UX which I've used for [git-mediate](https://github.com/Peaker/git-mediate/) is to have a single `GIT_MEDIATE_OPTIONS` environment variable which can then have `--port 5 --no-colors` content which is parsed exactly like the command line arguments. There could be an `optionsEnvVar "FOO_BAR_OPTIONS"` with a flag per option on whether it is available there (generally a setting on how you generally like things, like see colors in diffs or not should be in the options, but options to specify what to do should only be in cmd line opts)