Make server buffer writes

[kyrias]

Finally got around to looking at this again and realized that I was looking at it from completely the wrong end last time.

Fixes #199.

[jbr]

Could you add a bit more explanation of the fix? It's been a bit since I've looked at async-h1

[kyrias]

@jbr I'm not sure what more to add other than that the fix is to buffer writes to the socket. Why this is necessary should be described in the references issue.

But if you can say what you feel is missing from the explanation I can try to explain it better.

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Edit: I also just realized that this should probably also be done to the client side. Didn't even occur to me before since the only place I use it I end up using so rarely I never noticed whether the same thing happened. Guess I can try to do some tests later, but pretty sure the same thing should happen there.