Python version of Blewitt's MIDAS estimator, using numpy arrays
Original code in fortran: http://geodesy.unr.edu/MIDAS_release.tar
Reference: Blewitt et al. (2016): MIDAS robust trend estimator for accurate GPS station velocities without step detection, J. Geophys. Res. Solid Earth, 121, 2054–2068, doi:10.1002/2015JB012552.