Use an object, instead of an array of pairs, as a map

This is more idiomatic and shorter
remove line that did nothing (just assigned undefined)
Remove return from setColours since it's not a method

this will always just be the global object here.
use strict, because why not? Don't make formatHex global
fix inconsistent indentation style
support all css color names
Merge pull request #10 from ExplodingCabbage/master

Looks good.