Complete -w, --viewer argument properly
Add ImageMagick viewer example to config
Add changelog generation script, and makefile target
Version 1.3.1

Changelog:
- Complete -w, --viewer argument properly
  - Before, it would only complete if the option was the first
    positional parameter. Now it should complete regardless of where the
    option appears in the command line.
- Add example configuration for ImageMagick image viewer

Signed-off-by: Emil Lundberg <lundberg.emil@gmail.com>