When I'm building a web application in Go, I prefer to use command-line flags to pass configuration settings to the application at runtime. But sometimes, the client I'm working with wants to use environment variables to store configuration settings, or the nature of the project means that storing settings in a TOML, YAML or JSON file is a better fit. And of course that's OK — it makes sense to be flexible and vary how configuration is managed based on the specific needs of a project and/or...