Bridging golang / rust runner API

[jmwample]

In support of trying to get the water wasm binaries that we write to be truly pluggable we need to bridge some gaps in the way that the libraries use / label the exported water interface.

The goal of this issue is to be a discussion of what both sides are doing, why, and how we can make something that works for both generically.

[gaukas]

For now we are pending on v0(+) design doc, which is right the next thing I will be working on (based on Go's design).