envflag.go
func Bool(name string, value bool, usage string) *bool {
	return EnvironmentFlags.Bool(name, value, usage)
}
func Bool(name string, value bool, usage string) *bool {
	return EnvironmentFlags.Bool(name, value, usage)
}
// Bool defines a bool flag with specified name, default value, and
// usage string.  The return value is the address of a bool variable
// that stores the value of the flag.