Feature: Use socket error codes for connection rejections (#63 by @clue)

$promise = $proxy->connect('imap.example.com:143');
$promise->then(null, function (Exeption $e) {
    if ($e->getCode() === SOCKET_EACCES) {
        echo 'Failed to authenticate with proxy!';
    }
    throw $e;
});

Feature: Report matching SOCKS5 error codes for server side connection errors (#62 by @clue)

Fix: Fix SOCKS5 client receiving destination hostnames and fix IPv6 addresses as hostnames for TLS certificates (#64 and #65 by @clue)

Improve test suite by locking Travis distro so new defaults will not break the build and optionally exclude tests that rely on working internet connection (#61 and #66 by @clue)