Json struct c docs

[petrelharp]

I think that removing the json+struct C code from tskit itself and providing an example in the C docs is probably the way to go. @bhaller provided the C code, modified from the method and tests in #3437.

Currently this has the additional docs that are also in #3440.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 84 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.68%. Comparing base (2f26dc6) to head (c5c9157).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3439      +/-   ##
==========================================
- Coverage   91.92%   91.68%   -0.24%     
==========================================
  Files          37       38       +1     
  Lines       32153    32242      +89     
  Branches     5143     5158      +15     
==========================================
+ Hits        29556    29561       +5     
- Misses       2264     2348      +84     
  Partials      333      333              

Flag	Coverage Δ
C	82.30% <0.00%> (-0.41%)	⬇️
c-python	77.34% <ø> (ø)
python-tests	96.40% <ø> (+<0.01%)	⬆️
python-tests-no-jit	33.20% <ø> (-0.02%)	⬇️

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

Components	Coverage Δ
Python API	98.70% <ø> (+<0.01%)	⬆️
Python C interface	91.23% <ø> (ø)
C library	91.27% <ø> (ø)

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[petrelharp]

Codecov is complaining because the example C file is not being hit. AFAICT this is expected, and perhaps we should change this line to ask codecov to just cover c/tskit/ instead of c/?

[bhaller]

LGTM!

[petrelharp]

Indeed, none of the examples/ code is hit by codecov (as we'd expect, just verifying):

[petrelharp]

Merging this since it's been reviewed carefully by Ben H, after consulting with Jerome. I need to double-check the change to .codecov.yml hasn't messed something up; will do that in a separate PR.

[petrelharp]

I've checked in #3446 that the change to .codecov.yml didn't break codecov's c coverage.