C# Namespace Declaration

Hi Jae,

I've added a namespace declaration to the IDL to support code generation for a C# client that I've created. For now, I have a copy of the IDL in my project, but I think that it would be best to refer to the master copy in this repo.

If you'd like to have a look, my project can be found here: https://github.com/adamschmidt/suro-net