Add mkvfontvalidator

[moi15moi]

mkvfontvalidator would be a new command to verify if all the font files are muxed to the mkv.

It will automatically detect the muxed fonts and ass file by using the codec id.
To be compatible with mpv, we will use the same codec id as them. Codec id for ass file and codec id for font file.

Finally, mkvfontvalidator should have at least these options

  -mkv MKV
                        The video file to be verified. Must be a Matroska file.
  -mkvpropedit MKVPROPEDIT
                        Path to mkvpropedit.exe if not in variable environments. If -mkv is not specified, it will do
                        nothing.
  --need-draw-fonts
                        If specified, FontCollector will report a error if a font used in a draw isn't muxed to the mkv. For more detail when this
                        is usefull, see: https://github.com/libass/libass/issues/617