HTTP 1.1 use by default persistent connections

Hi, reopening the discussion about #834.

Now the HTTP server returns always the `Connection: keep-alive` that is NOT necessary in HTTP 1.1, 2 and 3.

We maintained it for faster HTTP 1.0 clients, that almost nobody use.
And the majority of clients and users have the penalty of that unnecessary extra header, that reduce performance and increase bandwidth of each request.
Also this header is added to the hosting bandwidth bill and the server is less eco friendly :).

I think that is better by default than don't send this header, and add property for HTTP 1.0 enabled that add this header, to anybody that need it.
Similar to now we have with the `reuseport` option now.
EDIT: better a property in `Workerman\Protocols\Http::$http10_persistent` .

Thank you.