v0.15.1

.gtui format 10 (reads v1..v10). Crate 0.15.1.

Fixed

• A zero-byte .gtui opens as a new document instead of failing with json: byte 0: unexpected end of input. touch empty.gtui && graph-tui empty.gtui now behaves like nvim: empty buffer,
  :w writes it. Any empty file (not just .gtui) is treated the same way, and --dump of one
  prints the blank document rather than an error.

• Editing text in place with double-width characters no longer swallows them. The draft was written
  one character per cell, so each CJK character's right half was overwritten by the next one; the
  caret column was counted in characters as well, so it drifted half a cell per wide character.
  Both now use display width: wide characters occupy two cells (the second is a blank continuation,
  like the static text path), and Up / Down keep the column in cells, landing on the character
  boundary at or before it -- the same rule nvim uses.