v1.4.0

• Using nullable reference types in API
• Added #pragma nullable to support nullable reference types in the emitted code
• Fixed handling of base types (no longer sorting the provided list) - see #3
• Added support for public, internal, sealed and abstract modifiers on messages
• Validate ProtoInclude attributes
• Added support for default and default(T) literals in default parameter values
• Forward parameters from immutable base types in the constructor
• Added support for generating nested classes