Proof of concept replacing managed C++ with pinvoke

Given the current time constraints and the potential rewrite of the core of REEF in C# instead of Java, we are considering using pinvoke to from standard C++ to call C# to move the current bridge to .NET Core as quickly as possible. This makes sense now as a rewrite of the core of REEF in C# should provide a completely asynchronous cross-language messaging API for the bridge based on Apache Thrift which provides full protocol definition and client-server stub code generation.