vf_aspect: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_blackframe: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_boxblur: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_crop: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_crop: cosmetics, break lines
vf_cropdetect: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_delogo: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_drawbox: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_drawtext: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_fade: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_fieldorder: cosmetics, remove an extra linebreak
vf_fieldorder: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_format: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_frei0r: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_gradfun: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_hflip: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_hqdn3d: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_libopencv: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_lut: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.
vf_overlay: use the name 's' for the pointer to the private context

This is shorter and consistent across filters.