I really like the idea of @bobtidey to have that fixed-name header file that may be present in a certain project or not and if it exists, it will be included in all library code files.
There are two reasons that make this my #1 approach:
Even if I have forked a library and included it for private use, I always have to change the library for different purposes (e.g. different OLED displays in different projects). Even that these lib- modifications are per-instance, it would be much cleaner to have that fixed-name header file that is part of the project - and thus, is naturally project specific - and leave the library completely untouched (read-only).
Second reason that this is a well known approach since most of the well-known IDEs have kind of a “project-properties” dialog that allows to specify project-level defines. The fixed-name header file would mimic the exact same behavior .
Jul’14 means July 2014. Thought is 14th of July 2016. But seems to be an open issue since i struggle with the exact same problem today in 2016 