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

   @app.route('/comment/', methods=['POST'])
   @log
   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))

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

   {% extends 'base.html' %}
   {% block title %}
       问答详情
   {% endblock %}
   {% block main %}
       <div class="box">
           <h3 href="#" >{{ ques.title }}</h3>
           <small> {{ ques.author.username }}<span class="badge" style="margin-left: 75%">{{ ques.create_time }}</span></small>
           <hr>
           <p>{{ ques.detail }}</p>
           <hr>
           <form action="{{ url_for('comment') }}" method="post">
               <div><textarea class="form-control" id="comment" rows="3" style="margin-left: 1%" name="new_comment" placeholder="write your comment"></textarea><br></div>
               <input type="hidden" name="question_id" value="{{ ques.id }}">
               <button type="submit" >发送</button>
           </form>
         <h4>评论:（{{ ques.comments|length }}）</h4>
            <ul class="list-unstyled">
               {% for foo in comments %}
                   <li class="list-group-item">
                       <a>{{ foo.author.username }}</a>
                       <span class="badge pull-right">{{ foo.create_time }}</span>
                       <p>{{ foo.detail }}</p>
                       <br>
                   </li>
               {% endfor %}
           </ul>
   
       </div>
   {% endblock %}