feature: add Module.print_hierarchy

[shareefj]

Adding a new Module method that prints the hierarchy. Useful for visualising the structure of a module.

I'm adding this PR mainly to start a conversation about where is best to do this sort of thing. I'd like to be able to pretty print some sort of hierarchy view of a design. It would be nice to be able to do something similar to how tree prints directory hierarchies but I haven't looked further that the simple indentation shown in this PR.

Should this go in the Module class or in the verilog module or in some new module?

[shareefj]

There do seem to be some nice options for pretty printing this but I'll leave that for another day. This simple indentation works for now I think. https://stackoverflow.com/questions/9727673/list-directory-tree-structure-in-python

[shareefj]

@sbourdeauducq Did the last push do what you were implying?

[sbourdeauducq]

It's better, there is still an issue with indent handling, just do the *4 multiplication at print time.

[shareefj]

Not sure what you mean. The multiplication is done at print time. Did you mean something else?

        if indent == 4:
            print(self.__class__.__name__)
        for name, submodule in self._submodules:
            if name is None:
                if not include_anon:
                    # all hierarchy below an anonymous module is skipped
                    continue
                name = "anon"
            print("{}{}:{}".format(" " * indent, name, submodule.__class__.__name__))
            submodule.print_hierarchy(indent+4, include_anon)

[sbourdeauducq]

The 4

[shareefj]

++verbosity