Minor Description
Right now the DescriptiveStatistics is for ResizableDoubleArray, but if the user has the double[] data she wishes to get DescriptiveStatistics for there is no way of doing this (besides the inefficient way of creating a ResizableDoubleArray from the double[]).
It would be possible to use StatUtils, but it does not contain near as much functionality as DescriptiveStatistics.
Idea: Create a DescriptiveStatistics for double[] also. I'm not sure which way of implementing it would be the best, but one way would be to make DescriptiveStatistics abstract with all but the apply-method implemented as now. The apply-method should be made as abstract which then has to implemented in the extensions together with a field containing the values. (addValue, windowSize etc. has to go in the ResizableDoubleArray-extension.) The double[]-extension should then have a constructor taking double[] as a parameter.
