c++版本支持熔断降级吗，demo里没看到相关的例子

[mcgrady-forever]

Issue Description

Type: bug report or feature request

Describe what happened (or what feature you want)

Describe what you expected to happen

How to reproduce it (as minimally and precisely as possible)

Tell us your environment

Anything else we need to know?

[sczyh30]

Refer #25