NANOGrav 12.5y KDE representation for Ceffyl

Reference: Lamb, Taylor and van Haasteren: The Need For Speed: Rapid Refitting Techniques for Bayesian Spectral Characterization of the Gravitational Wave Background Using PTAs

This is a downloadable KDE (Kernel Density Estimator) for the NANOGrav 12.5y dataset that can be used with the Ceffyl package.   Please see the GitHub page for Ceffyl installation details and usage information.