Added normality test

Uses D'Agostino's K-squared test to test for the normality of the
distribution of r’s. Returns the p-value for this test. If the r’s are
not normally distributed, then one of the assumptions of the Z-score
has not been met.
Correct way of accessing value from numpy matrix
Typo
The order variable is now in numpy

for the sake of consistency.
Added line breaks to separate functions
Changed 'order' variable to 'shuffle_order'