raw2bmx: add variable d10 frame size option
raw2bmx: add variable d10 frame size option

Added --var-size option to indicate that the raw D-10 bitstream
does not have fixed frame sizes and the frame size needs to be
parsed for each frame. E.g. use this option when using the --klv
option with MXF files that use KLV fill to achieve fixed frame sizes

Limecraft/ebu-bmx,xunchangguo/BMX,Limecraft/ebu-bmx,Limecraft/ebu-bmx,xunchangguo/BMX,xunchangguo/BMX