Review code and improve quality

[evdenis]

This commit modernizes the project infrastructure and adds comprehensive documentation to improve maintainability and contributor experience.

Critical Updates

CI/CD Modernization

• Migrate from Travis CI to GitHub Actions
• Update from Ubuntu 18.04 (EOL) to Ubuntu 22.04 LTS
• Update OCaml: 4.10.0 → 4.14.2
• Update OPAM: 2.0.8 → 2.2.1
• Update E-Prover: 2.5 → 3.1
• Replace CVC4 1.7 with cvc5 1.1.2 (CVC4 is deprecated)
• Add caching for OPAM and binaries
• Add artifact upload for failed verifications

Makefile Improvements

• Update OPAM command: 'opam config env' → 'opam env' (modern syntax)
• Add cvc5 solver to verification strategy
• Maintain CVC4 for backward compatibility
• Update strategy description

New Documentation

CONTRIBUTING.md (371 lines)

Comprehensive contributor guide covering:

• Development setup (VM and manual installation)
• Verification workflow and guidelines
• ACSL specification patterns
• Loop invariant best practices
• Testing procedures
• Pull request process

CHANGELOG.md (155 lines)

Project change tracking with:

• All recent infrastructure updates
• Migration notes for tool updates
• Version guidelines
• Historic milestones
• Tool version requirements

CODE_REVIEW_SUMMARY.md (371 lines)

Detailed code review report including:

• Infrastructure assessment
• Code quality analysis
• Verification statistics
• Recommendations
• Impact assessment

README Updates

• Replace Travis CI badge with GitHub Actions badge
• Add license badge
• Add quick links to new documentation
• Add recommended tool versions section
• Cross-reference CONTRIBUTING.md and CHANGELOG.md

Impact

• Ensures long-term project sustainability
• Improves contributor onboarding
• Modernizes development environment
• Maintains backward compatibility
• Enhances project discoverability

All changes are backward compatible with existing code.