Enforce username uniqueness.
Add views for user resource.
Use werkzeug.security for password hashing.

Also, hash the password in the User model so that any assignment to the
password field will be hashed immediately.
Add repr to models.
Add get-by-username class method.
Add missing self.
Change User.username to User.id comparison.
Convert User.get into regular function.
Use filter instead of empty string comparison.
Add username to sort fields.
Add missing marshal_user call.
Merge marshal_article and marshal_user.
Change User.username to User.id comparison.
Remove default argument from request.json.get.
Add __ne__ to User (as per documentation).
Add is_admin column to User.
Rewrite permissions decorators.
Add manage.py script.
Add pip requirements file.
Use new-style string formatting.