[Suggestion] Use .proto files to define CodedInputStream format

[hanabi1224]

I saw the library depends on Google.Protobuf, but it's not using .proto files to define/spec binary format, just curious what's the concern here. :)

[richardschneider]

It's technical debt and perhaps my bias not to have another step in building the library.

In Peer Talk I went with protobuf-net which uses C# attributes.

[hanabi1224]

Currently it's quite simple to setup the build step of .proto files, and it's actually my another question that why the library depends on both official protobuf and protobuf-net? Any chance to unify them? : )

To setup build step with official protobuf, just add below lines to .csproj

<ItemGroup>
    <Protobuf Include="**/*.proto" />
    <EmbeddedResource Include="**/*.proto" />
    <PackageReference Include="Google.Protobuf" Version="3.8.0" />
    <PackageReference Include="Grpc.Tools" Version="1.21.0" PrivateAssets="All" />
</ItemGroup>

[hanabi1224]

Just created a draft PR to unify protobuf dependencies richardschneider/peer-talk#37 Please let me know your concern