doc/filters: add few more examples for blend filter

Signed-off-by: Paul B Mahol <onemda@gmail.com>
Fix a crash on oom when decoding hevc.
aacdec: fix small comment, update decoder features comment
MAINTAINERS: add myself as libzvbi-teletextdec maintainer

Signed-off-by: Marton Balint <cus@passwd.hu>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>