common.h currently contains several things: Math macros, UTF-8 macros,
other fundamental macros; furthermore it also contains miscellaneous
math functions and it (directly and indirectly) includes lots of other
headers.

This commit moves the "other fundamental macros" to macros.h which is
a more fitting place.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>