wasmtime-wasi now supports using multiple snapshots to interface to the
same WasiCtx!
wasmtime_wasi::Wasi::new(&Store, WasiCtx) is a struct which owns your
WasiCtx and provides linkage to every available snapshot.
Individual snapshots are available through
wasmtime_wasi::snapshots::preview_{0, 1}::Wasi::new(&Store, Rc<RefCell<WasiCtx>>).