VAR : function to test if model is stable
DOC : fixed reference in var.is_stable()
SCoT : added function to calculate autocovariance matrices.
SCoT : added functions for testing VAR residuals against whiteness
SCoT : mvarica now returns sensor-space VAR coefficients and residuals.
SCoT : function for visualizing VAR residual whiteness test
SCoT : fixed off-by-one error
SCoT : plot_whiteness now returns the p-value
Tests : added unit test for whiteness check
Tests : (whiteness test) improved comments.
Examples : VAR model validation example
Examples : Added stability test to validation example