一个 慢速 流水号生成库，生成连续的数值流水号。灵感来自 SnowFlake 的 Go 语言实现。
生成的是流水号，可以用于订单类的系统。流水号像这样：
uid_test.go:33: 10002016061718222627096
uid_test.go:33: 10002016061718222627097
uid_test.go:33: 10002016061718222627098
uid_test.go:33: 10002016061718222627099
uid_test.go:33: 10002016061718222627101
uid_test.go:33: 10002016061718222627102
uid_test.go:33: 10002016061718222627103
uid_test.go:33: 10002016061718222627104
uid_test.go:33: 10002016061718222627105
uid_test.go:33: 10002016061718222627106
uid_test.go:33: 10002016061718222627107
流水号生成规则：
- 每毫秒最多产生 99（01 ~ 99）个 ID
- 前四位是 Worker ID
- 后二位是序号，不足两位，补零