a invtation token invite only once. a persion can set invitation times limit, '-1' means that has unlimited, '0' means that can't invite, '>0' means that has limited.
a invtation token invite only once.
a persion can set invitation times limit, '-1' means that has unlimited, '0' means that can't invite, '>0' means that has limited.

sundisee/Flask-User,sundisee/Flask-User