Add APIXU API for weather (public-apis#814)

Author: s-nirali

README.md

@@ -812,6 +812,7 @@ API | Description | Auth | HTTPS | CORS |
 ### Weather
 API | Description | Auth | HTTPS | CORS |
 |---|---|---|---|---|
+| [APIXU](https://www.apixu.com/doc/request.aspx) | Weather | `apiKey` | Yes | Unknown |
 | [ClimaCell Micro Weather](https://developer.climacell.co) | Historical, real-time and nowcast weather data | `apiKey` | Yes | Yes |
 | [Dark Sky](https://darksky.net/dev/) | Weather | `apiKey` | Yes | No |
 | [MetaWeather](https://www.metaweather.com/api/) | Weather | No | Yes | No |