Code cleanup

I've done some code cleanup.
I'm not finished yet, but I thought I'd open a request to get some feedback,
both from the auto-pulltester and from @WalterBright.

Please comment if such changes are ok (or even more, which changes are ok).
I'd like to do more, but I don't want to waste time on something that would be rejected anyway.

I think the next step would be using bool appropriately in method return types.
Additional suggestions?

A long-term goal could also be to separate frontend and backend in a better way.
IIRC we had bigger problems with ddmd cause there were dependencies from the frontend to the backend or something like that.