Lack of accuracy comparable with numpy

Current commited version of algorithm https://github.com/achains/Twist-n-Sync-CPP-Module/commit/759e1009411bbe4758578c1e77fff7882eefbceb loses to numpy & scipy in accuracy. 

Should pay attention to CubicSpline::getCoefficients()

![image](https://user-images.githubusercontent.com/56088401/127554910-838f5e57-3b90-46af-a6b8-14cc08afc2af.png)
