Add skin() helper mixin.

Sometimes design and engineering requirements mean that we need to:

output the colors for default color scheme and one or more additional color schemes into the same CSS file
and to control which color scheme is used via a "global" CSS class name set on the web pages's html or body element.

For example, the .my-complexion component may output a blue text color on most pages, but on pages with a <html class="skin-wicked-witch">, the .my-complexion component will output a green text color.

The Skin module will help with this requirement.

JohnAlbin / chroma

Add skin() helper mixin. #12