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'])
   @loginFirst
   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('questionDetail',question_id=ques_id))

   <form action="{{ url_for('comment') }}" method="post">
           <div class="pinglun">
               <textarea name="new_comment" class="form-control" rows="3" id="new-comment" placeholder="write your comment">
               </textarea>
               <input name="question_id" type="hidden" value="{{ ques.id }}"/>
           </div>
           <button type="submit" class="btn btn-default">发送</button>
       </form>
       <hr>
   
       <h4>评论：({{ ques.comments|length }})</h4>
       <hr>
   
   
       <ul class="news-list">
           {% for foo in ques.comments %}
               <li style="padding-left: 0px; padding-right: 10px; box-shadow: rgba(0, 0, 0, 0.5) 0px 0px 0px 0px;">
                   <span class="glyphicon glyphicon-leaf" aria-hidden="true" ></span>
                   <a href="{{ foo.author.username }}"></a>
                   <br>
                   <a href=" {{ url_for('questionDetail',question_id=foo.id)}}">{{ foo.title }}</a>
                   <span class="badgs">{{ foo.creat_time }}</span>
                   <p>{{ foo.detail}}</p>
               </li>
           {% endfor %}