2.17.0

Infrastructure

• Target C# 8.0
• Added .NET Standard 2.1 and .NET Core 3.1 support
• Enabled nullability analysis

Publishing

• Replaced repo.roscidus.com feeds with apps.0install.net

Misc

• Fixed manifest digest of some ZIP archives not matching the value calculated by Zero Install for Linux
• Replaced CliSubCommand abstract class with ICliSubCommand interface
• Use FeedUri instead of Uri for all Config properties
• Added support for detecting .NET Framework 4.6.2