KeplerFit fits a Keplerian velocity distribution model to position-velocity (PV) data to obtain an estimate of the enclosed mass. The code extracts the scales of the pixels in both directions, spatial and spectral, then extracts the most extreme velocity at each position; this returns two arrays of positions and velocities. KeplerFit then models the extracted PV data and returns a set of the best-fit parameters, the standard deviations in each of the parameters, and the total residual of the fit.