Test for symmetry of a (k, k) square contingency table
This is an extension of the McNemar test to test the Null hypothesis that the contingency table is symmetric around the main diagonal, that is
n_{i, j} = n_{j, i} for all i, j
Parameters:  table : array_like, 2d, (k, k)


Returns:  statistic : float
pvalue : float
df : int

See also
Notes
Implementation is based on the SAS documentation, R includes it in mcnemar.test if the table is not 2 by 2.
The pvalue is based on the chisquare distribution which requires that the sample size is not very small to be a good approximation of the true distribution. For 2x2 contingency tables exact distribution can be obtained with mcnemar