doc/filters: split luma/chroma descriptions for unsharp option

Honour declaration order in filter implementation, for shorthand
consistency.
doc/filters: introduce example in vflip filter
doc/filters: amend documentation for the hue filter

Make clear that the options accept an expression.
lavfi: add video stabilization plugins using vid.stab library

vidstabdetect and vidstabtransform common functions for interfacing
vid.stab are in libavfilter/vidstabutils.c

Signed-off-by: Georg Martius <martius@mis.mpg.de>
lavfi/vidstab: miscelenaous cosmetics and typo fixes.
lavfi/vidstab: consistent descriptions.
doc/filters: reword vidstab options intro.
lavfi/vidstab: add missing flags for 2 options.
lavfi/vidstab: make use of direct variable.
lavfi/vidstab: remove mention of defaults for consistency with other filters.
lavfi/vidstabdetect: fix direct path.

The frame must be writable if the show option is set, otherwise pass the
frame unchanged.
lavfi: add vidstabutils.h to SKIPHEADERS.

Fix checkheaders when vid.stab is not available.
lavfi: add timeline support in {de,remove}logo.

Both don't change anything in the context between frames.
vc1dec: redesign the intensity compensation

The existing implementation had little to do with VC1.
This could be implemented by adjusting the reference frames
ithemselfs but that would make frame multi-threading difficult.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
vc1dec: Implement intensity compensation for vc1_interp_mc()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
vc1: use use_ic instead of shuffling mv_mode around

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