Optimize images with oxipng 9.1.4

```
% oxipng -o max --strip safe mc-screenshot-cropped.png
Processing: mc-screenshot-cropped.png
161947 bytes (29.86% smaller): mc-screenshot-cropped.png

% oxipng -o max --alpha --strip safe mc-logo.png
Processing: mc-logo.png
14039 bytes (50.93% smaller): mc-logo.png
```

Author: zyv