Refactor color: Consolidate `case/when` statement.
Add a spec for #to_hsb, unsaturated color case.
Refactor Rustle::Color#to_hsb
Throw error when invoking hsb factory with invalid args.
Merge pull request #2 from jhamon/refactor-color

Thanks! Yeah, I haven't looked at this project in a while. Good call on the HSB class method.