Tag ristretto-0.3.0

- Re-introduce autorotation based on the exif-orientation tag, a
  regression since 0.0.93
- Prevent segmentation fault when an error occurs while loading
  an image
- Port image-viewer to cairo.
- Fix Bug #8097  (Prevent thumbnails from disappearing)
- Read the bgcolor properties on startup
- Let the file properties-dialog show file-properties.
- Add --settings cli-option to launch the settings-dialog.
- Add help->contents menuitem, launching documentation
- Add a user-manual
- Solve problem with size-calculation in size_prepared callback
- Set default height to 440px, Show all buttons on a vertically aligned
- Show thumbnailbar by default
- Show toolbar when closing images in fullscreen-mode
- Improve background-color of monitor-chooser
- Make 'hide thumbnailbar fullscreen' the default
- Cleanup some memory-leaks
- Fix rounding error that generates continues rewrites of the main
- Decrease buffersize when loading images, solves a problem with the
  JPEG pixbufloader.
- Rotate thumbnails.