Refactor weather forecast functions

[csparpa]

This will affect version 3.0 as it is a breaking change in the library API.

We need to normalise the weather retrieval functions to the naming pattern:

• forecast_at_place(self, name, forecast_granularity, [limit])
• forecast_at_coords(self, lat, lon, forecast_granularity, [limit])
• forecast_at_id(self, id, forecast_granularity, [limit])

where "forecast_granularity" can be either "3h" or "daily"

[csparpa]

# OLD SIGNATURE                                        # NEW SIGNATURE
three_hours_forecast(self, name)                       --> forecast_at_place(self, name, "3h", [limit])
daily_forecast(self, name, limit=None)                 --> forecast_at_place(self, name, "daily", [limit])

three_hours_forecast_at_coords(self, lat, lon)         --> forecast_at_coords(self, lat, lon, "3h", [limit])
daily_forecast_at_coords(self, lat, lon, limit=None)   --> forecast_at_coords(self, lat, lon, "daily", [limit])

three_hours_forecast_at_id(self, id)                   --> forecast_at_id(self, id, "3h", [limit])
daily_forecast_at_id(self, id, limit=None)             --> forecast_at_id(self, id, "daily", [limit])