Improvements in the Emacs manual

Improvements in the Emacs manual

* doc/emacs/custom.texi (Customization Groups)
(Changing a Variable, Browsing Custom, Customizing Faces): Fix
markup of keys.
(Changing a Variable, Saving Customizations): Update the
description of buttons in the Custom buffer.
(Face Customization): More accurate description.
(Specific Customization, Examining, Locals): Add blank lines in
the @table.  Reported by Michael Albinus <michael.albinus@gmx.de>
in emacs-manual-bugs@gnu.org.