DIP: The Deprecation Process

[Mike Parker]

This is another candidate to become DIP 1013. It standardizes the 
deprecation process for DMD, DRuntime and Phobos. It is currently 
in Draft Review and has had some discussion already, but I'd like 
to get a few more eyes on it before moving forward.

Please familiarize yourself with the intent of the Draft Review 
stage [1] and keep all feeback in the PR thread [2].

Thanks!

[1] 
https://github.com/dlang/DIPs/blob/master/PROCEDURE.md#draft-review
[2] https://github.com/dlang/DIPs/pull/108