Remove files that can't be processed for some reason (fix #112).
Add failed files to the cli summary.
Move Devnull to the utils module.
Merge branch 'remove-failed-files'
Use cached properties to simplify the access to exif metadata.
Fix unicode no more exist on py3.
Fix #118: allow passthrough of original files
Add myself to AUTHORS
Merge pull request #119 from pitrou/passthrough

Fix #118: allow passthrough of original files
Include plugins in the distributed package (ref #117).