doc/emacs copyedits re rectangle-mark-mode

* doc/emacs/killing.texi (Rectangles): Copyedits re rectangle-mark-mode.
(CUA Bindings): Mention rectangle-mark-mode.
Doc tweaks re multi-monitor

* doc/lispref/frames.texi (Multiple Terminals): Copyedits re multiple monitors.

* lisp/frame.el (frame-monitor-attributes, display-monitor-attributes-list):
Doc fixes.
* doc/lispref/windows.texi (Window Sizes, Resizing Windows): Copyedits.
Small doc/ fixes re @var usage.

* doc/emacs/cmdargs.texi (Misc X):
* doc/emacs/display.texi (Optional Mode Line):
* doc/emacs/misc.texi (emacsclient Options):
* doc/emacs/vc1-xtra.texi (VC Delete/Rename):
* doc/lispref/buffers.texi (Buffer List):
* doc/lispref/display.texi (Image Descriptors, Defining Images):
* doc/lispref/functions.texi (Core Advising Primitives):
Small fixes re @var usage.
Small copyedits for doc/lispref

* doc/lispref/display.texi (Scroll Bars):
* doc/lispref/modes.texi (Header Lines): Copyedits.
* doc/misc/vip.texi (Other Vi Commands): Markup fix.
* doc/lispref/commands.texi (Generic Commands): Copyedits.
doc/emacs small markup fixes

* doc/emacs/misc.texi (Sorting):
* doc/emacs/search.texi (Query Replace): Markup fixes.
* imenu.el (imenu-default-goto-function): Fix typo.