Section traces

[amoodie]

Develop new section types. Principally add effective PathSection, and the CircularSection and RadialSection types. There is still more to do here, but I have opened issues for the main points.

Todo

• finish implementation for RadialSection angles
• finish tests for RadialSection
• implement the DipSection or open an issue
• can the optional argument be streamlined better (simpler)? Open an issue
• section arguments need to work for actual dimensions of the arrays (xarray) not just indices. Open an issue to address this after Jay's Xarray support #23

[codecov-io]

Codecov Report

Merging #26 into develop will increase coverage by 1.42%.
The diff coverage is 99.50%.

@@             Coverage Diff             @@
##           develop      #26      +/-   ##
===========================================
+ Coverage    89.55%   90.97%   +1.42%     
===========================================
  Files            8        8              
  Lines         1254     1441     +187     
===========================================
+ Hits          1123     1311     +188     
+ Misses         131      130       -1     

Impacted Files	Coverage Δ
deltametrics/section.py	98.36% <98.92%> (+1.39%)	⬆️
deltametrics/utils.py	87.64% <100.00%> (+19.06%)	⬆️

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[elbeejay]

Nice stuff, the passing of the *args/**kwargs for the plotting is handy to have.

Ran into a minor issue with the origin of the radial section, but hopefully that is minor. Similarly I had a small suggestion about the L0 identification method and where/how it could be used.