Yang Bin

This modification has been tested with valgrind on Linux and no memory leaks were detected, whereas there were leaks before. It's very impressive, and I hope it can be merged...

release version 3.11.0: String view support for all functions working on object keys (e.g., [at](https://json.nlohmann.me/api/basic_json/at/) or [operator[]](https://json.nlohmann.me/api/basic_json/operator%5B%5D/)), avoiding unnecessary allocations.

> 新的nlohmann::json库的json类型定义与hv当前使用的有冲突，如果程序有一部分引入了json库，另一部分使用hv时会出现链接错误的问题 具体来说是新版的json类型模板参数最后多了一个`class CustomBaseClass = void`，导致符号不一致 我直接将cpputil/json.hpp替换成最新版本的json.hpp, 目前使用没有问题.