Reduce `nl_(before|after)_class` from 2 to 1 to avoid needless newlines added
between class forward declarations (which is a shame, I liked the old behavior
more).
There're places where manual intervention is still required as uncrustify
is not ideal (unfortunately), but at least one may rely on it to do the
right thing most of the time (e.g. when sending in a patch).
The style itself is quite different from what we had before but making it
uniform across all the codebase is the key. I also hope that it'll make the
code more readable (YMMV) and less sensitive to further changes.
