Async OPC-UA Macros

Part of async-opcua, a general purpose OPC-UA library in rust.

This defines a number of utility macros for encoding, decoding, and defining types to help write server and client software.

Currently defines:

• Event, a macro for deriving the Event trait on custom event types.
• EventField, a macro for deriving the EventField trait, used for types that can be part of OPC-UA events.
• FromXml, with the "xml" feature. Derives conversion from XML objects in NodeSet2 files.
• JsonEncodable, with the "json" feature. Derives streaming serialization using OPC-UA JSON.
• JsonDecodable, with the "json" feature. Derives streaming deserialization using OPC-UA JSON.
• BinaryEncodable, derives streaming serialization using OPC-UA Binary.
• BinaryDecodable, derives streaming deserialization using OPC-UA Binary.
• UaEnum, derives the UaEnum and a few other traits to make it easier to define custom OPC-UA enums.

Features

• json, adds the JsonEncodable and JsonDecodable macros.
• xml, adds the FromXml macro.