Add --listen-timeout-secs

[marioortizmanero]

Fixes #70. @thennothinghappened, please let me know if this solves your issue. You may be interested in this feature as well, @Aerion.

[marioortizmanero]

Should we also modify the default value? Or is it good enough at 100 ms? I did change it on my own setup to 50 ms, but not sure what the default should be.

Going from 100 ms to 50 ms on my system increases the maximum load when spamming a lot from 1.9% to 2.6% (very roughly). The difference is somewhat noticeable visually. I would say it's good enough for my case, since for this test I spammed it as much as I could, which isn't a realistic use-case.

Shall we use 50 ms? Also, is the documentation for the new flag ok? Too many details?

[Aerion]

Documentation looks good. Users probably expect quick responsiveness to the changes.
What do you think of changing it to 50ms, but adding a section in the README indicating what to do if the CPU usage is too high for the user?

[marioortizmanero]

Sounds good! I'll do that and release a new version.

[marioortizmanero]

I've just added a FAQ section, which I wanted to do for a long time anyway. That includes a question about CPU usage and insufficient latency.