Add Config::loadSystemConfigBlocking() to load default system config and support parsing DNS config on all supported platforms (/etc/resolv.conf on Unix/Linux/Mac and WMIC on Windows) (#92, #93, #94 and #95 by @clue)

$config = Config::loadSystemConfigBlocking();
$server = $config->nameservers ? reset($config->nameservers) : '8.8.8.8';

Remove unneeded cyclic dependency on react/socket (#96 by @clue)