Viper - 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.

Viper does the following for you:

1. Find, load, and unmarshal a configuration file in JSON, TOML, YAML, HCL, or Java properties formats.
2. Provide a mechanism to set default values for your different configuration options.
3. Provide a mechanism to set override values for options specified through command line flags.
4. Provide an alias system to easily rename parameters without breaking existing code.
5. Make it easy to tell the difference between when a user has provided a command line or config file which is the same as the default.