envflag.go
func Float64Var(p *float64, name string, value float64, usage string) {
	EnvironmentFlags.Float64Var(p, name, value, usage)
}
func Float64Var(p *float64, name string, value float64, usage string) {
	EnvironmentFlags.Float64Var(p, name, value, usage)
}
// Float64Var defines a float64 flag with specified name, default
// value, and usage string.  The argument p points to a float64
// variable in which to store the value of the flag.