Consider exposing the ic0 object

[lastmjs]

We are not exposing all of the underlying ICP System APIs directly to the developer. In fact, we have ripped a good chunk out. But some of these APIs might be useful to devs...could we easily expose the ic0 object in Rust, dynamically? The idea would be to have little to no maintenance or test burden for this functionality.

If this is not trivial to do, let's move it to 1.0.