Revert "Remove the need for HostRef<Module> (#778)"

This reverts commit 7b33f1c619.

Pushed a few extra commits by accident, so reverting this.

crates/api/examples/hello.rs

@@ -35,7 +35,7 @@ fn main() -> Result<()> {
 
     // Compiler the `*.wasm` binary into an in-memory instance of a `Module`.
     println!("Compiling module...");
-    let module = Module::new(&store, &binary).context("> Error compiling module!")?;
+    let module = HostRef::new(Module::new(&store, &binary).context("> Error compiling module!")?);
 
     // Here we handle the imports of the module, which in this case is our
     // `HelloCallback` type and its associated implementation of `Callback.