BREAKING: Don't convert units unless specifically requested.
This allows you to define preferred units per-item
in the configuration map.
BREAKING: Remove $default-units setting. See above.
Allow arbitrary adjustment functions
in the $sizes map,
e.g. 'my-size': 24px ('add': 12px),
where add is an available function
that will accept 24px, 12px as arguments.
Support first-class functions in Sass 3.5 (I hope).
$default-unitssetting. See above.$sizesmap, e.g.'my-size': 24px ('add': 12px), whereaddis an available function that will accept24px, 12pxas arguments.