colourdistance 0.9.11

Currently only contains two options, ciede94 and ciede2000, both weighted to (roughly) a [0,1] scale (actually possible to get very slightly above 1). Will add more. Both are my own implementations, and ciede94 is probably 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.