Update Killing chapter in Emacs manual. Other misc manual tweaks.

Update Killing chapter in Emacs manual.  Other misc manual tweaks.

* doc/emacs/killing.texi (Deletion): Add xref to Using Region.
(Yanking): Move yank-excluded-properties to Lisp manual.  Move C-y
description here.  Recommend C-u C-SPC for jumping to mark.
(Kill Ring): Move kill ring variable documentation here.
(Primary Selection): Copyedits.
(Rectangles): Document new command rectangle-number-lines.
(CUA Bindings): Note that this disables the mark-even-if-inactive
behavior for C-x and C-c.

* doc/emacs/mark.texi (Mark): Mention "active region" terminology.
(Using Region): Document delete-active-region.

* doc/lispref/text.texi (Yanking): Document yank-excluded-properties.

* doc/lispref/package.texi (Packaging Basics): The commentary should say how
to begin using the package.