Making an issue based on [some discussion](https://github.com/geany/geany/pull/2270#pullrequestreview-278747519) in #2270.

Any macros that only serve to shorten/obscure straightforward code should be marked as deprecated in the API/comments and eventually removed. This does not include macros which help prevent unexpected pitfalls like `foreach_document` which checks that the document is valid.

Remaining useful macros should also be deprecated but then redirected to UPPERCASE named versions of them.