Computes the KolmogorovSmirnof statistic on 2 samples.
This is a twosided test for the null hypothesis that 2 independent samples are drawn from the same continuous distribution.
Parameters:  a, b : sequence of 1D ndarrays


Returns:  D : float
pvalue : float

Notes
This tests whether 2 samples are drawn from the same distribution. Note that, like in the case of the onesample KS test, the distribution is assumed to be continuous.
This is the twosided test, onesided tests are not implemented. The test uses the twosided asymptotic KolmogorovSmirnov distribution.
If the KS statistic is small or the pvalue is high, then we cannot reject the hypothesis that the distributions of the two samples are the same.