This function is for conveinience of specifying knots for B-splines. Since the user usually only want to specify the interval that they are interested in the end knots are usually duplicated. This function interprets the first and last knots as the end points and duplicates them.
The knots including all interior and endpoitn knots
the order of the splines that the knots are to be used with. Defaults to 4, being cubic splines
A vector of knots with the order specified as an attribute