Env-canada

- Add type info for weather XML data and use typing when creating return value
- Switch from unparsed datetime to `datetime` object in output

- Make radar GIF frames per second configurable
- Make radar opacity configurable

- Remove ability to specify station for radar (only lat/lon supported)

- Switch to ECWeather class from ECData
- Split off AQHI retrieval into separate class
- Switch to asyncio from blocking IO
- Add tests