Add alternate VSYNC estimator algorithm

[mdrejhon]

A great alternate algorithm is published by @ad8e

https://github.com/ad8e/vsync_blurbusters/blob/main/vsync.cpp

He suggests that this is more accurate. I used Jerry's code simply because I needed JavaScript, and his was already JavaScript. However, he has released it as BSD-0, and should be a superior algorithm.