an array of control points, eg [{x:10,y:20}, {x:50,y:50}, {x:100,y:100}, {x:120,y:100}]. For a cubic bezier this should have four points.
a decimal indicating the distance along the curve the point should be located at. this is the distance along the curve as it travels, taking the way it bends into account. should be a number from 0 to 1, inclusive.
calculates a point on the curve, for a Bezier of arbitrary order.