extractplanes filter

Signed-off-by: Paul B Mahol <onemda@gmail.com>
lavfi/testsrc: add support for color interactive command
lavu: add planar 16 bit and 8 bit rgb with alpha

Signed-off-by: Paul B Mahol <onemda@gmail.com>
doc/filters: document asetpts in single place

Signed-off-by: Paul B Mahol <onemda@gmail.com>
eamad: Check against minimum supported dimensions

Fixes out of array reads

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>