This touched a lot more code than initially expected, for two reasons.
First, this broke a big RGBASM assumption: that sections are always being
written to at their end. This plus other problems required touching
basically the entirety of `section.c`.
Second, I tried different solutions to solve the above problem, and along
the way I cleaned up many things around. (I believe that keeping this to
"cleanup" commits yields subpar results, and since it's boring they get
postponed anyways.)
RGBLINK support still needs to be added, but this will come next.
As suggested by https://github.com/rednex/rgbds/issues/350#issuecomment-498030458
The order `count` then `byte` was decided after some discussion:
- First argument consistent with single-arg syntax
- Intuitive at least to some people other than myself
- Consistent with other assemblers, at least ca65
