Add timeout support to libhv adapter.

[michael-grunder]

Add timeout support to our libhv adapter.

See: #904

[michael-grunder]

cc @ithewei This is my attempt to add timeout support to your adapter. I'm unfamiliar with the library so please let me know if my usage is correct.

Edit: I think this logic isn't ideal if users update the timeouts multiple times (as it will add a bunch of timers). Is there a mechanism in libhv to find an already existing timer?

[ithewei]

cc @ithewei This is my attempt to add timeout support to your adapter. I'm unfamiliar with the library so please let me know if my usage is correct.

Edit: I think this logic isn't ideal if users update the timeouts multiple times (as it will add a bunch of timers). Is there a mechanism in libhv to find an already existing timer?

You are right, and you can use htimer_reset to update timeout multiple times.

[michael-grunder]

@ithewei If you don't mind taking a look at the new timeout logic that would be great. In reading the libhv source code I saw that there are several "built-in" timers in the hio_t structure, but it was unclear to me whether I could safely use any of them for this purpose.

@bjosv Let me know if anything jumps out at you. It should now be possible/efficient to update timeouts arbitrarily when using libhv.

[bjosv]

Nice!
Maybe example users would get helped by a comment in debugCallback() that we expect a NULL reply since DEBUG SLEEP should timeout..
..but it LGTM as is.