New setting to copy files from the source directory to the destination (ref #48)
Move check_or_create_dir to the utils module.
Bump 0.6.0
Prepare next version.
Fix thumbnail path check for directories without images (ref #68).
Fix stupid mistake in previous commit (ref #68).
More checks and logging for thumbnails (ref #71).
Fix issue with ExposureTime Exif tag when it is not a tuple (ref #76).
Refactor the way to handle albums and medias.
Update tests + small fixes.
Documentation
Fix to get thumbnail from sub-albums.
Use directly the `Album` object in the template.

- This allows to use all attributes of the album object.
- The meaning of the theme variables is more explicit.
Use the original file order to build the list of medias.
Update changelog
Merge branch 'refactor'
Skip empty directories.
New settings to define the sort order for albums and medias (closes #2).
New setting to disable autorotation of images, and warn about the
incompatibility between autorotation and EXIF copy (ref #72).
Comment default value in the settings template.