Remove dangerous operators

[sea-kg]

WsjcppYamlItem &operator[](int idx) { return *(this->getElement(idx)); }
WsjcppYamlItem &operator[](const std::string &sName) { return *(this->getElement(sName)); }

Dangerous because if user keep static object so then it will be destruct.

Redesign to WsjcppYamlCursor algorithm;