This PR follows apache#8668, with splitting
out interfaces class and terminal ast-dump implementation.

This visualizer is aimed for quick look-then-fix, so the interface is
simple. Despite that, customization is still possbile through
implementing interfaces defined in `interface.py` or overriding existent
implementations inside a renderer module, like `terminal.py`.

A tutorial is also provided in this PR.

A graphviz renderer will also be contributed after this PR.