m doc

Signed-off-by: Mattias Andrée <maandree@operamail.com>
ramps => ramps16

Signed-off-by: Mattias Andrée <maandree@operamail.com>
info: ramps => ramps16

Signed-off-by: Mattias Andrée <maandree@operamail.com>
add 8-bit ramps (good for software gamma)

Signed-off-by: Mattias Andrée <maandree@operamail.com>