Define a wasi/wasm Runtime object
To do a full port, we'll need an implementation of Runtime
with support for running in a wasi and/or wasm environment.
This might be possible based on future tokio/async_std work, but there's a way to go; see #20 (closed) for discussion.
It might also be necessary to define a new Runtime
from scratch based on WasmRuntime
or something.
See also #343 for issues surrounding lacks of arbitrary TCP sockets.