Simulate a and Sab from full conditional distributions under bin likelihood
raSab_bin_fc(Z, Y, a, b, Sab, SS = round(sqrt(nrow(Z))))a square matrix, the current value of Z
square binary relational matrix
current value of row effects
current value of column effects
current value of Cov(a,b)
number of iterations
new value of Z
new value of Sab
new value of a