ENH: add centroid method for angles

[bifbof]

Fix #437.
Such that centroids can be calculated for angles that pass over the -180, 180 wrapping border.

[codecov]

Codecov Report

Base: 98.06% // Head: 98.08% // Increases project coverage by +0.01% 🎉

Coverage data is based on head (e13b865) compared to base (d3ade20).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #453      +/-   ##
==========================================
+ Coverage   98.06%   98.08%   +0.01%     
==========================================
  Files          39       39              
  Lines        1858     1877      +19     
  Branches      261      263       +2     
==========================================
+ Hits         1822     1841      +19     
  Misses         14       14              
  Partials       22       22              

Impacted Files	Coverage Δ
trackintel/preprocessing/positionfixes.py	98.78% <100.00%> (+0.02%)	⬆️
trackintel/preprocessing/staypoints.py	99.01% <100.00%> (ø)
trackintel/preprocessing/util.py	100.00% <100.00%> (ø)

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[henrymartin1]

Looks really good, thanks for the fix!
I have a small comment for the test and didn't you mention in the error report that the same error applies here. Then we should fix this as well, shouldn't we?

[henrymartin1]

Great work, thanks for the changes!