x86/swr: add SSE2/AVX pack_8ch functions

Reviewed-by: Michael Niedermayer <michaelni@gmx.at>
Reviewed-by: Ronald S. Bultje <rsbultje@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>
avcodec/loco: Support LOCO reference encoder with odd width

Fixes Ticket1221

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
doc/filters: document bit-depth independent cropdetect limit

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