speed up some obvious common cases

Dependencies

• [2] RJGZD4IN binary search to most natural up/down with proportional fonts
• [3] JS6JSYOT online contextual help
• [4] IYW7X3WL left/right cursor movement, deleting characters
• [5] 3CS5KKCI up/down cursor movement
• [*] OTIBCAUJ love2d scaffold

Change contents

• replacement in main.lua at line 549
  [3.615]→[2.339:404](∅→∅)
  − cursor_pos = nearest_cursor_pos(lines[cursor_line], old_x)
  [3.615]

  [3.1510]
  + cursor_pos = nearest_cursor_pos(lines[cursor_line], old_x, cursor_pos)
• replacement in main.lua at line 555
  [3.813]→[2.467:532](∅→∅)
  − cursor_pos = nearest_cursor_pos(lines[cursor_line], old_x)
  [3.813]

  [3.913]
  + cursor_pos = nearest_cursor_pos(lines[cursor_line], old_x, cursor_pos)
• replacement in main.lua at line 715
  [2.783]→[2.783:820](∅→∅)
  − function nearest_cursor_pos(line, x)
  [2.783]

  [2.820]
  + function nearest_cursor_pos(line, x, hint)
• edit in main.lua at line 719
  [2.856]

  [2.856]
  + local max_x = cursor_x(line, #line+1)

  + if x > max_x then

  + return #line+1

  + end

  + local currx = cursor_x(line, hint)

  + if currx > x-2 and currx < x+2 then

  + return hint

  + end
• edit in main.lua at line 728
  [2.889]

  [2.889]
  + if currx > x then

  + right = hint

  + else

  + left = hint

  + end