Add option to fhb to set the accept-headers to allow compression

When I ran performance tests for Java Performance Tuning, I needed to be able to compare compressed vs. uncompressed output, so I added this change to fhb to set the accept-encoding mime type via a new -z option.

Also this allows fhb to report the 95th% and 99th% response times in addition to the 90th% repsonse time.