http://api.openweathermap.org/data/2.5/weather?zip=92618&appid=d9d6b642ca88454a3396830792d4b9a7
// write our own temperature history function, take
// * date
// * zip
// as the input parameter, return the
// * temperature for the date for that zip.
// we are only allow to use this openwathermap api to query today's weather
// that means, if we didn't retrieve the weather yesterday, we cannot return it, simply return something to the caller.
// as first step, let's use global variable to save all history weathers