Improve C11 coverage

[jquast]

• introduce C11 sub-sections in introduction
• Combine C11 and python coverage for reporting
• Improve C11 coverage

[codspeed]

Merging this PR will not alter performance

✅ 119 untouched benchmarks

---

_{Comparing jq/C11-coverage (f8a70d8) with master (9b9cfd8)}

[codspeed]

Merging this PR will not alter performance

✅ 119 untouched benchmarks

---

_{Comparing jq/C11-coverage (d23df82) with master (06ac438)}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.50%. Comparing base (9b9cfd8) to head (f8a70d8).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##            master     #270       +/-   ##
============================================
- Coverage   100.00%   87.50%   -12.50%     
============================================
  Files           27       41       +14     
  Lines         2040     5593     +3553     
  Branches       473     1494     +1021     
============================================
+ Hits          2040     4894     +2854     
- Misses           0      323      +323     
- Partials         0      376      +376     

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