SmoothStep (generalized)

Generalized version of the smooth step indicator (originally posted here : SmoothStep). 

This version is using a property of a smooth step that it can be further smoothed – based on Kenneth H. Perlin’s (a professor in the Department of Computer Science at New York University) idea

• when order 0 is used, it is the same as built in stochastic / 100 (with slowing in stochastic set to 1)
• when order 1 is used, it is the same as the smooth step indicator
• when any higher order is used, it filters further the signal while keeping the values in the expected ranges

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