Refactoring the dmd ast

[tripleo1]

ref: https://github.com/dlang/dmd/blob/master/CONTRIBUTING.md#how-you-can-help

Why don't you write a program to do this?

Celebrate Your Contribution: Take pride in being a part of this significant compiler development effort!

I put this in Show and tell to showcase the fact that I am not putting my money where my mouth is.

[dkorpel]

Writing such a program seems more work than doing the refactoring manually, but I invite anyone to try.