colourdistance 1.0.7

Currently only contains three options (ciede 76, ciede94, and ciede2000), all weighted to (roughly) a [0,1] scale (actually possible to get slightly above 1). Will add more. All are my own implementations (although ciede2000 is based on a several dozen implementations found during research), and they may be wrong because of it. Thanks go out to Josh Clayton (https://robots.thoughtbot.com/get-your-c-on), for helping me to understand the structure I was attempting to acheive.