Go configuration with fangs

 Viper is a complete configuration solution for Go applications
 including 12-Factor apps. It is designed to work within an application,
 and can handle all types of configuration needs and formats.
 It supports:
 .
  * setting defaults
  * reading from JSON, TOML, YAML, HCL, and Java properties config files
  * live watching and re-reading of config files (optional)
  * reading from environment variables
  * reading from remote config systems (etcd or Consul), and watching changes
  * reading from command line flags
  * reading from buffer
  * setting explicit values
 .
 Viper can be thought of as a registry for all of your applications
 configuration needs.