doc: Copyright in CSS, CSS split in 2 files

Reviewed-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/mjpegdec: fix rounding of chroma_height

Fixes green line at the bottom
Fixes Ticket3913

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