Simplified feed id generation and added support for url fragments

Changes:
- Simplified the  unique_id generation of a feed item
  - The new ids contain now two `/` more, one at the beginning of the path section and one at the end.
  - The new ids also support now url fragments (e.g. An entry located at `http://test.de/index.html#fragment` gets now the id `tag:test.de,{date}:/index.html/fragment` instead of `tag:test.de,{date}:index.html`)
- Updated unittest output to match the new ids