Function unescape

3rd/json/include/nlohmann/json.hpp:9209–9213

unescape "~1" to tilde and "~0" to slash (order is important!)

    /// unescape "~1" to tilde and "~0" to slash (order is important!)
    static void unescape(std::string& s)
    {
        replace_substring(s, "~1", "/");
        replace_substring(s, "~0", "~");
    }

    /*!
    @param[in] reference_string  the reference string to the current value