Support Image Thumbnails

[kj800x]

I recently ran into a case where I needed to support thumbnails for my images too, so that I'm not sending so many bytes over the wire for listing pages. It was easy enough to extend thumbsupply to support images using the convert program from the imagemagick software.

Using the convert program with the resize argument, we can generate a thumbnail with the same aspect ratio that fits within the specified dimensions. For example, convert infile.png -resize 240x240 outfile.png will create a file with the same aspect ratio as infile.png but fitting within 240x240.

test/test-image.png is in the public domain. I have downloaded it from publicdomainpng.com. test/test-animated-gif.gif is downloaded from wikimedia commons and it's listed as being in the public domain: https://commons.wikimedia.org/wiki/Category:Animated_Earth#/media/File:BlackMarble_2016_rotating_globe_at_night_transparent.gif

To generate thumbnails of images, the computer will need Imagemagick installed. I've noted this in the Readme.