Some of these were made possible by moving several common macros to
libavutil/macros.h.
While just at it, also improve the other headers a bit.
Reviewed-by: Martin Storsjö <martin@martin.st>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
(This is actually the second time the encoder stuff is removed;
the first was in 8b4119187b.)
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
