Coroutine\PostgreSQL->connect

建立postgresql 非阻塞的协程连接

function Coroutine\PostgreSQL->connect( string $connection_string);

example:

go(function () {

    $a = new Swoole\Coroutine\PostgreSQL();
    $conn  = $a -> connect ("host=127.0.0.1 port=5432 dbname=test user=wuzhenyu password=");
	var_dump($conn);
});