Refactoring + DSN support
* Support DSN in client library (fromDsn) * Use arguments vs options in CLI for required input * Use common `BaseCommand` for all CLI commands * Support .env in CLI * Update README.md
* Support DSN in client library (fromDsn) * Use arguments vs options in CLI for required input * Use common `BaseCommand` for all CLI commands * Support .env in CLI * Update README.md