Long shadow SASS mixin

SASS mixin to produce long shadows. Long shadow is created out of multiple dropped shadows. It produces text or box shadow based on parameters:

• $length (default: 100) - length of the shadow, the unit is extracted and used in further computations
• $color (default: rgba(128, 128, 128, 0.05)) - color of the shadow
• $stepX (default: 0.5) - the X distance between dropped shadows (value between 0 and 1 means more created shadows), negative value can be used
• $stepY (default: 0.5) - the Y distance between dropped shadows (value between 0 and 1 means more created shadows), negative value can be used
• $blur (default: 1) - blur parameter for created shadows