Add support for IGC format

[efa]

IGC files are generated by Flarm, LXnav instruments, Colibrì and others. Are waypoints files.
Can be good support at least as input, best would be output too.
GPSbabel manage them:
$ gpsbabel -i IGC -f 2016-04-24_Valerio.IGC -o CUP -F 2016-04-24_Valerio.cup
Will provide some example files and documentations on format

[efa]

a basic example is here:
https://xp-soaring.github.io/igc_file_format/index.html
while complete documentation can be found here:
https://xp-soaring.github.io/igc_file_format/igc_format_2008.html
I cannot find the official page on FAI web site about IGC

[efa]

here the official doc:
https://www.fai.org/sites/default/files/igc_fr_specification_2020-11-25_with_al6.pdf