Documentation and implementation of blacklist deletion.

- added comments
- refactoring of the request/response handling due to
http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
- deleting blacklists is now possible
- a blacklist is now a blackset (^-^) so no duplicated entries may be
stored
- accessing a blacklisted entry via GET will now return 200 or 204
depending on whether the resource exists or not