6.0.0

• Drop net461 target
• Add net462, net6.0, and netstandard2.1 targets
• Update NodaTime and TimeZoneConverter dependencies
• Update to latest CLDR, IANA, and other data sources
• Use System.Text.Json instead of Newtonsoft.Json
• Update public interfaces to use read-only collections and dictionaries where appropriate
• Ensure results are ordered correctly, where appropriate
• Add nullability annotations
• Several performance updates

Internally:

• Use C# 10 throughout
• Update project structure
• Add Verify snapshot tests
• Add GitHub Actions CI