envflag.go
func Uint64(name string, value uint64, usage string) *uint64 {
	return EnvironmentFlags.Uint64(name, value, usage)
}
func Uint64(name string, value uint64, usage string) *uint64 {
	return EnvironmentFlags.Uint64(name, value, usage)
}
// Uint64 defines a uint64 flag with specified name, default value,
// and usage string.  The return value is the address of a uint64
// variable that stores the value of the flag.