Having a choice with a defined set of options is nice, but it
also requires these options to be #defined somewhere _before_
entering config.h. To keep class-like encapsulation, we'd need
two header files for each code unit, one for the options, another
one for the usual header.
That said, we use other examples of such options, e.g. CPU, F_CPU
or KINEMATICS. For CPU and F_CPU it works fine, because their
options are numbers or other values known by the compiler. For
KINEMATICS it kind of works, because this #define is used in only
one place ... and there it's suboptimal already, because no option-
set.
Anyways, I was unsure about this change and if it turns out to be
a poor decision later, it can be reverted.
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