title: Sum of all .png sizes
body: <p>Is there any possibility to sum all .png sizes in folder ? I know there is a function <code>file.size()</code> but it does not exactly match my expectations. I want to have function which input is a folder and in output I have sum of all .png files within it. Alternatively is there any function as <code>file.size()</code> but which refers to folders (<code>folder.size()</code>) ?</p>