pass Net::Server log_file option via %extra

This gets rid of a ternary with an empty list as its false case that
otherwise clutters a static list of key/value pairs and makes it not
seem so bad that the values in the list are aligned much too far away.
pass Net::Server log_level config option via %extra

After the previous commit, the logging-related options are pulled apart.
Also, log_level defaults to 2 so it’s not necessary to pass that value.
So this patch moves it next to the log_file logic and sets it only when
DEBUG has been set.
simplify port binding logic
support SSL
Merge pull request #77 from ap/revisited-ssl

IO::Socket::SSL-based SSL support, based on overhauled ::Proto::SSL in Net::Server 2.0 series