Reduce MAKE_ACCESSORS code duplication via a new header.

Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>
MAINTAINERS: add Alexander Strasser for the server

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avfilter/vf_perspective: factor u cliping code

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>