envflag.go
func Float64(name string, value float64, usage string) *float64 {
	return EnvironmentFlags.Float64(name, value, usage)
}
func Float64(name string, value float64, usage string) *float64 {
	return EnvironmentFlags.Float64(name, value, usage)
}
// Float64 defines a float64 flag with specified name, default value,
// and usage string.  The return value is the address of a float64
// variable that stores the value of the flag.