suggestion: make loading config from env optional #418

When I add the project as a dependency, it'll require env var access for PGAPPNAME, PGDATABASE, PGHOST, PGOPTIONS, PGPASSWORD, PGPORT, PGUSER regardless I prefer to use this way of providing configuration or not. I consider allowing access to all env vars via --allow-env as a security risk and runnig with --allow-env=PGAPPNAME,PGDATABASE,PGHOST,PGOPTIONS,PGPASSWORD,PGPORT,PGUSER is pretty unconvinient.

So WDYT about considering a way to opt-out from auto-config via env vars?