Provide e2e browser sdk example

It is not obvious how to use @assemblyscript/loader with the browser sdk example, I had to download the loader separately but I see there are some instantiate bits in the dist sources but they're not exported or I can't figure out how to do it.

It would be helpful if we had a full(but simple) e2e example where the compiled binary gets instantiated and used using the loader and maybe also show some passing data back and forth to give the user a head start.