Optimize struct field order to reduce memory usage

[ksw2000]

1. Reduce RequestHeader from 368 bytes to 360 bytes
2. Reduce Request from 816 bytes to 800 bytes
3. Reduce Response from 432 bytes to 416 bytes
4. Reduce Client from 312 bytes to 288 bytes
5. Reduce HostClient from 416 bytes to 392 bytes
6. Reduce PipelineClient from 176 bytes to 168 bytes
7. Reduce pipelineConnClient from 216 bytes to 208 bytes
8. Reduce Cookie from 232 bytes to 224 bytes
9. Reduce FS from 184 bytes to 160 bytes
10. Reduce fsHandler from 168 bytes to 160 bytes
11. Reduce ResponseHeader from 328 bytes to 320 bytes
12. Reduce headerScanner from 128 bytes to 120 bytes
13. Reduce TCPDialer from 104 bytes to 96 bytes
14. Reduce workerPool from 152 bytes to 144 bytes

[erikdubbelboer]

Thanks!

[gaby]

@erikdubbelboer I figured this was also affecting bytebufferpool, and it is. So I sent a PR for that repo. https://github.com/valyala/bytebufferpool/pull/29