add colorize

[daddygongon]

What a fantastic idea! I will use this in my class since next Wednesday after changing the text. Would you add the 'color' for 'red, green, refactoring' ? While this makes the codes dirty, I usually teach students "Color makes things simpler"

[peterc]

There is another PR under review which changes the layout of these methods, so we might need to hold this one back until that's sorted out, but I do like your idea!

However, one change I will need to make is to make this an optional feature which depends upon whether colorize is installed or not. I don't want testrocket to force anyone into extra dependencies, but if colorize is installed, I am happy for it to be used :-)