Expose interfaces of an import Wasm module by macro

[mikevoronov]

At the moment, to import Wasm module into service project, it's necessary to list all it's interfaces in code. But it could be difficult to do since a Wasm module could contain a lot of export functions. The more handy way to do that is to introduce a new macro that could collect all export functions from a Wasm binary and expose them to code.

[ValeryAntopol]

Should we use build.rs instead? This feature was designed exactly for that.

Also, do we need to load modules from network, like in #133 ?