Create an endpoint to search wheater predictions

[alustau]

• Create unit tests
• Create an endpoint where users can search for a city and find the weather
  predictions for that city for the current day, and for any day in the upcoming 10 days.
• It should not be possible to search for dates in the past.
• It should not be possible to search dates greater than the current day + 10 days.
  Today is 01/01/2018. Searching for data from 11/01/2018 is ok.
  Today is 01/01/2018. Searching for data from 12/01/2018 is not ok.
• The temperature that is shown to users is always the an average we collect from our
  partners:
  TempPartnerA = 2, TempPartnerB = 2, TempPartnerC = 5​ =>​ Average = ​ 3
• Users of the API should always get the latest version of the prediction, as provided by
  our partners.
• Predictions must be shown on Celsius and Fahrenheit scales.
• You should show data in a human readable format.