Adds catmull_rom as an example for --scale in the user manual, alongside
a brief description of the filter.
catmull_rom was only exposed to users as an available filter through
--scale=help. However, catmull_rom is very often aliased as "Bicubic" in
other applications such as GIMP and VapourSynth, and is a relatively
popular resizing filter. The documentation lacked any description of
catmull_rom, outside of a brief mention of it in the --tscale section.
dokur0chan
e15619e70d