Added support for $weather (experimental).

Added support for $weather (experimental).

Download, parse and display METAR data from the NWS.

icao must be a valid icao for the required location
(see for instance https://pilotweb.nas.faa.gov/qryhtml/icao/).

data_type must be one of the following:

last_update   : display the date (yyyy/mm/dd) and time (UTC)
	        of the last update.
temperature_C : display air temperature in degree Celsius.
temperature_F : display air temperature in degree Fahrenheit.
cloud_cover   : display the highest cloud cover status.
pressure      : display air pressure in millibar.
wind_speed    : display wind speed in km/hour.
wind_dir      : display wind direction.
wind_dir_DEG  : display compass wind direction.
humidity      : display relative humidity in %.
weather       : display any relevant weather event (rain, snow, etc.).

delay_in_minutes (optional, default 30) cannot be lower than 30 min.
Up to 3 stations can be simultaneously queried.

Use --enable-weather to compile this in.