Feature Request: better rendering

As a numba-rvsdg user and as a developer, I want to be able to view an SCFG both from the terminal.

The proposed API should perhaps look like:

```
scfg.view()
```

And then, if we are in an IPython notebook environment render the SCFG inside the notebook and if we are in a Python or IPython terminal session, attempt to render the SCFG to a PDF files and open it in an existing viewer.