Completed the package entry point's name change from edit-picture to

Completed the package entry point's name change from edit-picture to
picture-mode.
(move-to-column-force, picture-end-of-line): When movement is completed,
scroll horizontally if necessary to make point visible.
(picture-beginning-of-line): New function.  Exists to force horizontal
scrolling if the buffer is wide.
(picture-mode-map): Instead of rebinding common keystrokes, use
substitute-key-definition to remap all keystrokes attached to the
corresponding commands.