Implement timer / delay function

[lpereira]

Implement a lwan_delay(request, ms) function that will yield from the coroutine and resume it whenever that timer expires. Might need to use timerfd_create() or something else. Might also be an opportunity to investigate libev, libevent and libuv.

[lpereira]

Finally fixed this one with 5a145e5b4e3ab09c21d85d5a7d290a812990e66a