Delay between probes

[anton-dutov]

Any option to configure dalay between probes, like ping command

[jcgruenhage]

I don't think it's necessary to implement that in this library directly, because doing it outside of it is quite easy too, using the interval stream provided by tokio directly. You can take a look at an example implementation over at https://git.jcg.re/jcgruenhage/peshming/src/commit/44251fa2f78bda24997952f267c1616a9affb3cc/src/ping.rs#L59-L67