feat: the RFC 6901 "-" array suffix is now supported

[fredbi]

Pointer.Set may append elements to an array using this syntax.

On Pointer.Get / Pointer.Offset it is always an error per RFC 6901 §4.

• fixes Consider implementing "-" as per RFC6901 #120

Change type

Please select: 🆕 New feature or enhancement|🔧 Bug fix'|📃 Documentation update

Short description

Fixes

Full description

Checklist

• I have signed all my commits with my name and email (see DCO. This does not require a PGP-signed commit
• I have rebased and squashed my work, so only one commit remains
• I have added tests to cover my changes.
• I have properly enriched go doc comments in code.
• I have properly documented any breaking change.

[codecov]

Codecov Report

❌ Patch coverage is 86.02151% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.15%. Comparing base (635e674) to head (cd06b0b).
⚠️ Report is 2 commits behind head on master.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
pointer.go	85.05%	8 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #121      +/-   ##
==========================================
- Coverage   82.53%   82.15%   -0.39%     
==========================================
  Files           2        2              
  Lines         292      353      +61     
==========================================
+ Hits          241      290      +49     
- Misses         35       42       +7     
- Partials       16       21       +5     

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