WASM: Run a WASM binary on Wasmtime

[mbestavros]

We'd like to build out a series of demos for our progress on Enarx's WASM support.

The first of these demos is simple:

1. Load a basic WASM binary. (Specifically, adding two numbers together.)
2. Run it through Wasmtime.
3. Display its output.

Whether we want to add any more on top of that (automation, compiling WASM) is up for discussion.

[mbestavros]

Worth noting this demo is more or less completed over on my repo.

I think there are a few enhancements to be made; right now, the number output is a bit verbose, and most of the setup code can be moved into the main function.

[mbestavros]

Resolved by #9; the repo now has a basic Wasmtime demo.