[Issue211] Added calc_LOS_length_in_isoflux()

[Didou09]

Three functions added to tf.geom.Rays:

• calc_length_in_isoflux() : compute the length inside a set of isoflux surfaces of each LOS
• calc_min_geom_radius(): compute the minimal geometrical radius (impact parameter) of each LOS
• calc_min_rho_from_Plasma2D(): compute the minimum normalized radius (or any field with a minimum on the axis) for each LOS

Fixes, in devel, issue #211

[pep8speaks]

Hello @Didou09! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2019-10-08 11:20:06 UTC

[codecov-io]

Codecov Report

Merging #212 into devel will decrease coverage by 0.05%.
The diff coverage is 12.5%.

@@            Coverage Diff             @@
##            devel     #212      +/-   ##
==========================================
- Coverage   44.14%   44.09%   -0.06%     
==========================================
  Files          71       71              
  Lines       21296    21327      +31     
==========================================
+ Hits         9401     9404       +3     
- Misses      11895    11923      +28

Impacted Files	Coverage Δ
tofu/version.py	100% <100%> (ø)	⬆️
tofu/geom/_core.py	63.47% <9.67%> (-0.58%)	⬇️

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