Implement iterator for JSONHashTable and JSONArray

Created by: shreyasbharath

Something like this -

for ( auto i = jsonHashTable.begin(), i != jsonHashTable.end(); i++ ) {
    cout << "Key " << i->first;
    cout << "Value" << i->second;
}

for ( auto i = jsonArray.begin(), i != jsonArray.end(); i++ ) {
    cout << "Value" << *i;
}

I think this will involve writing a custom iterator (see http://www.cplusplus.com/reference/iterator/) for these two classes, hopefully it isn't too difficult.