Name folder using url hash

- Instead of naming each segment using the url we instead append hash
  to the path
- The cat command was adapted accordingly since the file name no longer
  holds the hash
* Also fixed the default filename prefix for the Downloader
Fix docs and style

- Fixed a couple of docstrings
- Changed style based on pylint
Increase retries and add backof sleep

- Raise number of retries to 4
- We sleep before retrying, based on the
  retry count (3,9,27)s respectively