Added some vimdiff bindings and disabled folding by default when
launching vimdiff. Reorganized the keyboard bindings to make htem easier
to find and read. You can now trigger most of the cut commands by
hitting the <Leader> key (backslash) first to avoid replacing the
paste-buffer. A bunch of commands and toggles that made sense to do so
now work in all three modes. All folds can be toggled with <shift-F12>.
The command to turn tabs into spaces has been added. A few settings
added earlier today were tweaked or removed.