[dmd-internals] Refactorings of dmd

[Walter Bright via dmd-internals]

We have a big problem with dmd:

https://issues.dlang.org/buglist.cgi?bug_severity=regression&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&list_id=201147&query_format=advanced

A large and rapidly growing regression list. Something is going seriously wrong.

We've also had a number of very large refactorings of dmd code. I do not see how 
this has improved anything. In fact, they make things worse by making it hard to 
trace through what went wrong, as the code is all shuffled around.

(Vladimir has done a great job in isolating which pull requests caused which 
regression.)

Until this gets under control:

1. There will be no more refactorings unless approved by myself.

2. I want to focus on cutting down that regression list, not adding ever more 
features.