Allow the diff Stream Evaluator to operate on the rows of a matrix

Currently the diff function performs serial differencing on a numeric vector. This ticket will allow the diff function to perform serial differencing on all the rows of a matrix. This will make it easy to perform correlations on a matrix of differenced time series vectors using math expressions.

A screen shot is attached with diff working on a matrix of time series data. The effect is powerful. It removes the trend from a matrix of time series vectors in one simple function call.