Add v5.6.1 to CHANGELOG

Edit CHANGELOG for v5.6.0 release

Also removed previous entries because they were wrong.
TODO: Rewrite CHANGELOG

Fix indentation in release.sh

Refactor Attacker.hit and simplify tests

Simplify logic in Attacker.hit

Update CHANGELOG

Extract and test Histogram logic

Remove whitespace

Don't treat 3xx status codes as errors

Fixes tsenart#88

Add freebsd and windows releases