Colour

While writing Go Pixels Fight! I needed to be able to mix two colours to produce an average of the two to show which colour was winning; during my research I stumbled upon the color helpers in polished.js and while they didn't work for what I needed I thought it would be useful to myself in the future and others if they were ported to Go.

Primarily as a learning exercise in how to write tests with Golang I release this port to the wild in the hope that it may be of some use to someone.