Add tint-shade color stack

Allow users to create a stack that includes both shaded and tinted versions of
a color at the same time.

Not sure how you want to approach things like the conjoin method that @scottkellum helped with – there didn't seem to be a global place to put it.

sample output:

![sample output: tint-shade-stack](http://i.imgur.com/v7pPAFI.png)