add weather API

[aaronpk]

given a lat/lng, return information about the current weather at that location:

• temperature
• humidity
• pressure
• "feels like" temperature
• wind / wind gust
• rain in the last hour
• icon URL that represents current state (cloudy, raining, sunny, etc)

Use weather icons from https://erikflowers.github.io/weather-icons/

Weather data from wunderground