Testing

[delatrie]

Context

This PR sets up a testing infrastructure for allure-csharp packages. It also includes a set of Allure.NUnit tests to verify the infrastructure.

A checklist to complete:

• On-build sample generation
  • One solution per test project
  • One project per sample
  • Multifile samples
  • Patterns (razor)
  • Test against a project
  • Test against a NuGet package
  • independent target framework
  • independent dependency versions
• Optimization: pre-run build/test of samples
• Optimization: incremental build of samples
• Cleanup
• Sample runner (test setup routine)
• Data link (FS/pipes)
• Assert-only mode
• A set of test result assertions
• Allure.NUnit tests
• CI
  • target NuGet packages
  • pre-test all samples
  • assert-only

Closes #362.