GitLab

* doc/emacs/basic.texi:
* doc/emacs/calendar.texi:
* doc/emacs/display.texi:
* doc/emacs/mini.texi:
* doc/emacs/misc.texi:
* doc/emacs/picture-xtra.texi:
* doc/misc/info.texi: Prefer <PageDown> and <PageUp> over
<next> and <prior>.  Add missing @kindex entries.

* doc/emacs/custom.texi (Function Keys): Fix and add missing
key symbols.