User
====

A ``User`` object represents either a student, a supervisor,
or an academic assistant.  Since all users of this system have similar
basic information, such as username and email, we represented them all
as ``User`` object, and restrict their behaviors according to a field ``role``.

Each ``User`` object has following attributes:

``username`` : ``string``
   A unique name with which the user can refer to one another.
   It is also the primary key and allows the user to sign in.

``name`` : ``string``
   The legal name of the user.  This is required for group members to recognize
   each other, and for the academic assistants to collect their results.

``email`` : ``string``
   The email address that is used to contact with the user.

``password`` : ``string``
   The password for the user's account, encrypted with a hash function.

``role`` : ``string``
   The role of the user in this system.  It can be:

   - ``student``: Students who are participating in a group project or internship.
   - ``supervisor``: The supervisor of project(s).
   - ``assistant``: The academic assistant of a department.

``department`` : ``string``, *optional*
   The department of the user, such as ``ICT``, ``SA``, or ``LS``.
   Required for students and assistants.

``student-id`` : ``string``, *optional*
   Only applicable for users with role ``student``:
   A unique identifier assigned to students to be used outside this system.

``bio`` : ``object``, *optional*
   A markup text describing the user.  This is not necessary, but it can be
   helpful for a supervisor to have a biography to show their credibility in
   their respective field.