set return value of ts_bspline_buckle to the new index k such that [u_k, u_k+1]
set return value of ts_bspline_buckle
to the new index k such that [u_k, u_k+1]

this allows the user to draw the left/right part
of a split without using ts_bspline_evaluate function

msteinbeck/tinyspline,msteinbeck/tinyspline,retuxx/tinyspline,msteinbeck/tinyspline,pellaeon/tinyspline-example,arneboe/tinyspline,arneboe/tinyspline,pellaeon/tinyspline-example,msteinbeck/tinyspline,msteinbeck/tinyspline,msteinbeck/tinyspline,msteinbeck/tinyspline,msteinbeck/tinyspline,retuxx/tinyspline,retuxx/tinyspline