v0.1.0

Added

• Add utility to create class-based api views.
• Add last_visit_at field to ShortUrl schema.

Changed

• Convert all api views except for the /auth/ endpoints to class-based views.
• Update get_by_username() method of User model to comply with the constraints of the
  username field on user creation (handled by the ConstrainedUsername field type).

Removed

• Remove redundant get_by_origin() method of ShortUrl model.