Add client and server port logging

I have added both client and server port numbers as we can see them both being useful in some cases. You will see the functions to obtain port numbers are performed on every call to write_accesslog. It would be less overhead to perform this in the constructor and store as private member variables - if you prefer that I will update the code.
It would be better to get rid of stringstream, because it is very slow.
Formatting second and millisecond part separately, and joined them with "." results faster processing. Like this:

```cpp
        auto t = std::chrono::duration_cast<std::chrono::milliseconds>
          (std::chrono::high_resolution_clock::now() -
           lgsp->request_start_time).count();

        auto frac = util::utos(t % 1000);
        auto sec = util::utos(t / 1000);
        if(frac.size() < 3) {
          frac = std::string(3 - frac.size(), '0') + frac;
        }
        sec += ".";
        sec += frac;

        std::tie(p, avail) = copy( sec.c_str(), avail, p);
```