* commands.texi (User Input): Rewrite. Describe Emacs' behavior

* commands.texi (User Input): Rewrite.  Describe Emacs' behavior
directly, rather than in the context of ASCII.  Move description of
special properties of modifier key to new Modifier Keys node.
(Keys): Copyedit.
(Text Characters): Delete node.  Multibyte is the default nowadays, and
the node contents are obsolete.

* custom.texi (Modifier Keys): New node.

* emacs.texi (Top): Update node list.