lavfi/unsharp: add check on matrix x/y size values oddity
lavfi/unsharp: directly access in-loop variables in apply_unsharp()

Increase performance, to match mp=unsharp.
lavfi/unsharp: merge definition and declaration in init_filter_param()
lavfi/unsharp: add missing NULL check
lavfi/mp: drop mp=unsharp filter

The native filter is equivalent from the point of view of the features
and of performances.
lavfi/mp: drop mp=kerndeint filter

The filter has been natively integrated into libavfilter.
lavc: mark bitmap based subtitles codecs as such.
lavc: support subtitles character encoding conversion.
lavfi/subtitles: split options between ass and subtitles.
lavfi/subtitles: support charenc option.
lavfi: rename vf_ass.c to vf_subtitles.c
lavfi/subtitles: set a different description between ass and subtitles.
lavc/utils: reindent in avcodec_decode_subtitle2() after f7963993.
tests: fix values for the unsharp test

Set odd size for unsharp matrices, even values are not accepted.
lavc: fix codec_descriptor and pkt_timebase doxy.
lavf/subtitles: error out in case of bitmap subtitles.