The `pdftex` utility that is used for PDF documentation generation does
not support GIF images.
This fix replaces the animated `ReelBoard-Blinky.gif` with an animated
PNG (APNG) image `ReelBoard-Blinky.png`.
Note that APNGs are backwards compatible with "normal" PNGs. Modern
web browsers will display APNGs in the same way as animated GIFs, while
any application that can read PNG files can read APNG files
successfully.
Signed-off-by: Chris Pearson <ctpearson@gmail.com>
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