InitUser: Create a user account.
================================

Implement this function:

.. function:: InitUser(username string, password string) (userdataptr *User, err error)

    * Creates a User struct, initializes all necessary data within the struct and returns a pointer to it.
    * The User struct should include all data the client needs to operate on behalf of this user.
    * If a user with the same username already exists, return an error.

    :param username: Username
    :type username: string
    :param password: Password
    :type password: string

    :rtype: userdataptr, error

.. warning::
    Do not forget that your design must satisfy **all** requirements, including:
    
    #. The client application must be stateless (see
       :ref:`requirement_stateless`).
    
    #. Users can have multiple active user sessions at once (see
       :ref:`requirement_user_sessions`).