Added naive Users system

Added abortIfNotExists method and user resource

Added users resource on API

Added a model to prevent fake/spam users.

-Changed the user-creation method, now needs 2 steps to complete.
-Added url /createUser to activate users using a key.
-Added a method which generates random codes

Added passwords

Fixed wrong spelling

Removed white-lines and solved user-creation conflicts.

updated README.rst

PEP8 Refactor

Added Mozilla Hacks' article about Shiva

Typos in documentation

Added /about resource

MediaDir objects check existence of paths

PEP8 and some cosmetic changes

Renamed VERSION to __version__

Added contributors list to /about resource

Added subtitle to Clients

Added Shiva4J client

Client authors are now lists