Add support for frac data

[mraspaud]

This PR adds "FRAC" to the list of supported transfer modes for LAC data.

[codecov[bot]]

Codecov Report

Merging #115 (d615d1f) into main (fe4b883) will increase coverage by 0.92%. The diff coverage is 100.00%.

:exclamation: Current head d615d1f differs from pull request most recent head 2ecad40. Consider uploading reports for the commit 2ecad40 to get more accurate results

@@            Coverage Diff             @@
##             main     #115      +/-   ##
==========================================
+ Coverage   72.93%   73.85%   +0.92%     
==========================================
  Files          32       30       -2     
  Lines        2830     2689     -141     
==========================================
- Hits         2064     1986      -78     
+ Misses        766      703      -63     

Impacted Files	Coverage Δ
pygac/lac_reader.py	94.73% <100.00%> (+15.78%)	:arrow_up:
pygac/reader.py	79.43% <100.00%> (ø)
pygac/tests/test_reader.py	98.31% <100.00%> (+0.04%)	:arrow_up:
pygac/__init__.py
pygac/utils.py

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[mraspaud]

@helgaweb any comments?

[helgaweb]

@mraspaud Looks good. You might want to change the documentation here as well https://github.com/pytroll/pygac/blob/fe4b88377d991330074692402dee4beeed7ee3e1/pygac/reader.py#L223

[mraspaud]

thanks!