Editing widget using the interior of a window object.
Supports the following Emacs-like key bindings:
Ctrl-A Go to left edge of window.
Ctrl-B Cursor left, wrapping to previous line if appropriate.
Ctrl-D Delete character under cursor.
Ctrl-E Go to right edge (stripspaces off) or end of line
(stripspaces on).
Ctrl-F Cursor right, wrapping to next line when appropriate.
Ctrl-G Terminate, returning the window contents.
Ctrl-H Delete character backward.
Ctrl-J Terminate if the window is 1 line, otherwise move to start
of next line.
Ctrl-K If line is blank, delete it, otherwise clear to end of line.
Ctrl-L Refresh screen.
Ctrl-N Cursor down; move down one line.
Ctrl-O Insert a blank line at cursor location.
Ctrl-P Cursor up; move up one line.
Move operations do nothing if the cursor is at an edge where the
movement is not possible. The following synonyms are supported where
possible:
KEY_LEFT = Ctrl-B, KEY_RIGHT = Ctrl-F, KEY_UP = Ctrl-P,
KEY_DOWN = Ctrl-N, KEY_BACKSPACE = Ctrl-h