The word “highbright” was spelled as “hightbright” in a few places.

When use [lf](https://github.com/gokcehan/lf) to list files, emacs-libvterm may
read partial multi-byte character, for example:

  $ echo -n '招聘' | hexdump -C
  00000000  e6 8b 9b e8 81 98

  ; get "招", control sequence and partial character
  (vterm--filter process "\xE6\x8B\x9B\e[14;111H\xE8")

  ; now full "聘"
  (vterm--filter process "\x81\x98")

This will send "\xE8" to libvterm which is not a full character.

Allow using different background and foreground colors for same ANSI
index, analogously to how term-mode does it.

Remove magical indices for underlined cells with default foreground and
inverse-video cells with default background.  Instead, pass relevant
info to lisp function to handle these cases at higher level.

* elisp.c, elisp.h (Fapply): New binding.
(vterm_get_color): Add new argument for optional attributes.
* vterm-module.c (cell_rgb_color): Pass relevant attributes to
vterm_get_color.
* vterm.el (vterm--get-color): Use foreground or background color of the
face depending on received attributes.
* README.md: Update documentation