This function summarizes estimated spsur objects. The tables in the output
include basic information for each equation. The report also shows other complementary results
corresponding to the SUR model like the (GxG) covariance matrix of the residuals of the
equations of the SUR, the estimated log-likelihood, the Breusch-Pagan diagonality test or the Marginal
Lagrange Multiplier, LMM, tests of spatial dependence.