weights: Generating splines weights
In ivmte: Instrumental Variables: Extrapolation by Marginal Treatment Effects

This function generates the weights required to construct splines of higher order. This function was coded in accordance to Carl de Boor's set of notes on splines, "B(asic)-Spline Basics".

1	weights(x, knots, i, order)

`x`	vector, the values at which to evaluate the basis function.
`knots`	vector, the internal knots.
`i`	integer, the basis component to be evaluated.
`order`	integer, the order of the basis. Do not confuse this with the degree of the splines, i.e. order = degree + 1.