Query the system for maximum listen() backlog size
Set SO_REUSEPORT on master socket

It might be a good idea to implement some command-line parameter or other
tunable to control the creation of I/O threads (number, affinity, etc).
Reduce the coroutine context to 80 bytes on x86_64

Instead of using gregset_t, use an array of 10 uintptr_t.
Remove #include <unistd.h> from lwan-coro.h