Provide plugin implementation examples in different languages

[CromFr]

Ideally the examples should not depend on the nwnx4 codebase (i.e. can be built without cloning and building and nwnx4).
RPC client examples in different languages would be helpful too (once xp_rpc is merged).

• C
• C++
• Rust
• Go
• D (@CromFr )
• Other languages?

Those examples should be stored in separate Github repositories (so we don't dramatically increase the number of dependencies for nwnx4)

[scottmunday84]

Maybe the RPC folder should be expanded into a new repository and we attach it to NWNX4 as a submodule. Plenty of possibilities. I'm trying to find this one Apache project that allows you to take a pseudo code and build out the code in different languages. I figure that will make it easy to build out implementations and clients for gRPC through a build.