Add script to print the time the image was taken

The time the image was taken doesn't appear to be stored in the EXIF
data so this relies on the filename containing the timestamp.

This is used alongside a script (to be committed separately) that prints
a caption on to the images.
Add script to embed captions in images

I can use this in conjunction with the 'print-taken-at' script to embed
the date and time images were taken into the image itself. I'm planning
to do this for the latest image that I then grab as my desktop
background.

The image magick foo came from
http://www.imagemagick.org/Usage/annotating/#anno_on.