Added
* Added unit tests!
* (3, 7) - Decoding/encoding of SYNOP section 4 is now implemented
Fixed
* (4, 5) - Better handling of sunshine and radiation groups in SYNOP section 3
* (6) - Better exception handling
* `time_of_ending` in `weather_info` (SYNOP section 3, 901xx) now re-encodes correctly
* SYNOP section 3, 965xx now decodes correctly
* Multiple mirages can now be decoded and encoded (SYNOP section 3, 991xx)
* Latitude and longitude in `station_position` now returned as floats instead of strings
* `quadrant` checked for validity
* Instrumental `wind_waves` are now decoded from SYNOP section 3 group 1 and group 7 correctly