Add varying curve scale utilizing AnimationCurve and free alpha channel

[polynaught]

Evaluating an AnimationCurve at the resolution step intervals returns a float which can be packed into the alpha of the texture (_CurveTexture) that is currently not used.
Inside the shader the alpha value can be sampled and multiplied with _PlanarScale.
This opens up the possibility to play with different scales along the curve and adds more "life" to organic shapes.