feat: ability to edit status messages

[valchulen]

I'm in need to change the message associated with the status of a request. In my context: when millions of RPS are answered with 204, every byte of the response counts towards reducing AWS transfer out costs, so "NC" instead of "No Content" is a small change with big impact.

To do so, I've created SetStatusMessage. Also I've extracted the set of the statusLines to reuse it in said function.

I await for you input! Thanks!

[erikdubbelboer]

I don't think this is a good idea. I would rather add a statusLine []byte field to ResponseHeader and methods to set it. And when it's set it should be used here, otherwise use the current code:

fasthttp/header.go

Line 1642 in 81fc968

dst = append(dst, statusLine(statusCode)...)

[erikdubbelboer]

You also need to reset h.statusLine in the Reset method.

[erikdubbelboer]

Thanks!