Fix problems related to missing pol argument when using calc_R_from_A, also did some minor cleanup of example notebook

[cchwala]

• fix Polarisation info is not used correctly in processing shown in example notebook #115
• fix Do not use cml.A.where(cml.A > 0, 0) to set values smaller zero to zero #117

Things that were done in this PR:

• it is now forced to pass pol to calc_R_from_A when passing f_GHz, which is the way we commonly use this function. One can also pass a and b parameters instead of f_GHz and pol. There are now also tests that check this behavior.
• The WAA function waa_leijnse_2008_from_A_obs and waa_pastorek_2021_from_A_obs which use calc_R_from_A internally, have been adjusted to require a pol argument.
• Docstrings of the functions have been adjusted and also improved in some parts
• tests have been adjusted accordingly and new tests added
• black formating in files that were touched in this PR
• updated notebook on basic example workflow
  • use pol correctly (which is no enforce anyway, see above)
  • removed some unnecessary cells
  • improves some markdown text
  • changed the way resampling to 5-min and 1-h is done, which we do now after concatenating the list of CML Datasets to one large Dataset because resampling is much faster like this
  • made plotting of interpolated maps a bit nicer (in my opinion)
  • made plotting of time series more consistent (same figure width, removing unnecessary labels, better colors in some places)
  • use cml['A'].values[cml.A < 0] = 0 instead of cml['A'] = cml.A.where(cml.A > 0, 0), see Do not use cml.A.where(cml.A > 0, 0) to set values smaller zero to zero #117
  • added interpolation of short gaps in trsl, up to 5 minutes, which improves comparison with reference for high rain rates (I think we had this interpolation in the example notebook some time ago, but maybe it was removed to replace it with the more sophisticated blackout gap filling, which is not there yet..)

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.08 🎉

Comparison is base (bcc59ff) 71.62% compared to head (e8bb815) 71.71%.

❗ Current head e8bb815 differs from pull request most recent head 103a9bf. Consider uploading reports for the commit 103a9bf to get more accurate results

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #116      +/-   ##
==========================================
+ Coverage   71.62%   71.71%   +0.08%     
==========================================
  Files          28       28              
  Lines        1008     1011       +3     
==========================================
+ Hits          722      725       +3     
  Misses        286      286              

Flag	Coverage Δ
unittests	71.71% <100.00%> (+0.08%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pycomlink/processing/k_R_relation.py	78.84% <100.00%> (+1.29%)	⬆️
pycomlink/processing/wet_antenna.py	100.00% <100.00%> (ø)

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[nblettner]

Looks fine to me. I only marked some typos and a small possible extension in the docstrings.

[cchwala]

@nblettner thanks for the feedback. I adjusted the code accordingly.

Sorry, that I forgot to push my last update of the notebook. It is now here in 21ed485. I just removed cells were all code was commented out. I also change the relevant parts of the code to use the solution with cml.A.values[cml.A.values < 0] = 0, see #117 (we can change to a different solution once we agree which one is the best...)