Add addStringToObject with String to aJSON Library

[rei-vilo]

Add addStringToObject with String to aJSON library. Up to now, it only accepts const char* s.

    void addBooleanToObject(aJsonObject* object, const char* name, bool b);
    void addTrueToObject(aJsonObject* object, const char* name);
    void addFalseToObject(aJsonObject* object, const char* name);
    void addNumberToObject(aJsonObject* object, const char* name, int n);
    void addNumberToObject(aJsonObject* object, const char* name, double n);
    void addStringToObject(aJsonObject* object, const char* name, const char* s);

From Energia project