ver 3.3.7
* Enable image processing on background terminals.
* Improve the performance of processing images on 8 or less bpp framebuffer.
* Support SGR 5, 9, 21, 25 and 29.
* Support DECFRA, SL and SR.
* Starting mlterm with -j option executes mlclient if daemon process has already
  started.
* Change the maximum number of "U+XXXX-XXXX" in ~/.mlterm/(t,v,)(aa)font
  from 7 to 511.
* Add "unlimted" to "Backlog size" entry in mlconfig.
  Add "UNICODE (ARABIC)" and "UNICODE (EMOJI)" to "Font name" entry.
* Add --it/it_color, --bl/bl_color and --co/co_color options.
* Add --itfont/use_italic_font option.
* Add --bisep/bidi_separators option.
* Add --fullwidth/unicode_full_width_areas option.
* Add --working-directory/working_directory option.
* Add --deffont option.
* Disable "_HALFWIDTH" suffix in ~/.mlterm/(t,v)(aa)font files.
* Drop --ucsprop/use_unicode_property option.
* Bug fixes:
  Fix the failure of saving font configurations from mlconfig.
  Fix the bug which sometimes causes the failure of searching closest colors on X/8bpp.