Escape ` and ' in doc

Escape apostrophes and grave accents in docstrings if they are
are supposed to stand for themselves and are not quotes.  Remove
apostrophes from docstring examples like ‘'(calendar-nth-named-day
-1 0 10 year)’ that confuse source code with data.  Do some other
minor docstring fixups as well, e.g., insert a missing close
quote.

lisp/emacs-lisp/eieio.el

@@ -683,12 +683,12 @@ This class is not stored in the `parent' slot of a class vector."
   "Make a new instance of CLASS based on INITARGS.
 For example:
 
-  (make-instance 'foo)
+  (make-instance \\='foo)
 
 INITARGS is a property list with keywords based on the `:initarg'
 for each slot.  For example:
 
-  (make-instance 'foo :slot1 value1 :slotN valueN)")
+  (make-instance \\='foo :slot1 value1 :slotN valueN)")
 
 (define-obsolete-function-alias 'constructor #'make-instance "25.1")