Improvements + bug fix

Thanks @mknadler ;

• adds -ms- prefix to @mixin scale for free IE9 support
• adds variables to @mixin shadow
• adds default duration and standardizes capitalization of @Mixins scaledown, scale up, fadein
• moves functions black and white to directly under opacity
• switches names of center-h and center-h—unk for accuracy
• bug fix double @@ on l.263