title: Adding alpha channel to RGB array using numpy
body: <p>I have an image array in RGB space and want to add the alpha channel to be all zeros. Specifically, I have a <code>numpy</code> array with shape (205, 54, 3) and I want to change the shape to (205, 54, 4) with the additional spot in the third dimension being all 0.0's. Which numpy operation would achieve this?</p>