urls控制器

路由分发include('blog.urls')): 将以指定名称开头的url分发到指定app中去匹配
   urlpatterns = [
       url(r'^admin/', admin.site.urls),
       url(r'^blog/', include('blog.urls')),]  # 将以/blog开头的url分发到blog app下的urls中去匹配.