Handle Flickr links with /in/<what> in the URL

Now handles flickr.com
- `/user/photoid` (links to size 'c' - medium 800px width)
- `/user/photoid/in/<something>` (/in/<something> is kept)
- `/user/photoid/sizes/<size>/in/<something>` (unchanged)
Merge pull request #329 from dshafik/master

Handle Flickr links with /in/<what> in the URL