Sknat

I needed a REST API that allowed me to do more requests on the database than allowed in sandman, the reason why i did the following changes to the code:
- I added comparisons, limit, ... to the things you're able to query through GET requests (in retrieve_collection)
- added sql join support for n tables (also modifying a bit data structure)
- I stumbled on the etags problem (functions missing), but it got corrected within the week, so i got back to the development version.
- add views support (was one of the solutions in order to be able to view sql join)
I only tested it with a postgres database, but I think these new functionality could be interesting other sandman users, the reason why I'm submitting this.