Fix doc strings in ispell.el

Fix doc strings in ispell.el

* lisp/textmodes/ispell.el (ispell-check-version)
(ispell-get-casechars, ispell-get-not-casechars)
(ispell-get-otherchars, ispell-get-many-otherchars-p)
(ispell-get-ispell-args, ispell-get-extended-character-mode)
(ispell-get-coding-system, ispell-word, ispell-get-word)
(ispell-pdict-save, ispell-command-loop, ispell-help)
(ispell-filter, ispell-highlight-spelling-error)
(ispell-change-dictionary, ispell-region, ispell-ignore-fcc)
(ispell-get-line, ispell-message): Doc fixes (bug#71532)