Implementation of a Principal Curve Algorithm

This is an attempt to (re-)implement the principal curve algoithm in https://www.lri.fr/~kegl/research/PDFs/KeKrLiZe00.pdf in Python. I wanted to try to apply it to smooth center line point detections from autonomous car front cameras to estimate a more stable center line reference.

However, the implementation is not finished yet (I guess 15% may be missing to reach a testable state).