完成评论功能

1. 定义评论的视图函数
   @app.route('/comment/',methods=['POST'])
   def comment()：
   读取前端页面数据，保存到数据库中
2. 用<input type="hidden" 方法获取前端的"question_id" 
3. 显示评论次数
4. 要求评论前登录
5. 尝试实现详情页面下的评论列表显示

   @app.route('/comment/',methods=['POST'])
   def comment():
       comment = request.form.get('new-comment')
       ques_id = request.form.get('question_id')
       auth_id = User.query.filter(User.username == session.get('user')).first().id
       comm = Comment(author_id = auth_id, question_id=ques_id ,detail=comment)
       db.session.add(comm)
       db.session.commit()
       return  redirect(url_for('detail'))

   <input type="hidden"  name="question_id" value="{{ques.id}}" />

   <h4>评论:({{ ques.comments|length }}) </h4>

   @app.route('/comment/',methods=['POST'])
   @loginFrist
   def comment():
       comment = request.form.get('new-comment')
       ques_id = request.form.get('question_id')
       auth_id = User.query.filter(User.username == session.get('user')).first().id
       comm = Comment(author_id = auth_id, question_id=ques_id ,detail=comment)
       db.session.add(comm)
       db.session.commit()
       return  redirect(url_for('detail',question_id=ques_id))

   <ul class="list-unstyled">
                   {% for foo in comments %}
                       <li class="list-group-item">
                           <a>{{ foo.author.username }}</a>
                           <span class="badge pull-right">{{ foo.creat_time }}</span>
                           <p>{{ foo.detail }}</p>
                           <br>
                       </li>
                   {% endfor %}
               </ul>