Minor spelling and grammar fixes (bug#34756)

Minor spelling and grammar fixes (bug#34756)

doc/misc/cc-mode.texi (Style Variables, Customizing Indentation):
doc/misc/ede.texi (Extending EDE, ede-project-placeholder)
(ede-target, ede-proj-target, ede-compilation-program, ede-compiler)
(ede-linker): Remove apostrophe from possessive "it's".
doc/lispintro/emacs-lisp-intro.texi (Find a File):
doc/misc/gnus-faq.texi (FAQ 2-2): Write "an other" as a single word.
doc/misc/gnus.texi (Article Buttons):
lisp/gnus/gnus-art.el (gnus-button-mid-or-mail-heuristic-alist)
(gnus-button-mid-or-mail-heuristic): Write singular number of
Message-IDs, rather than plural.
lisp/gnus/message.el (message-user-fqdn): Capitalize initialism.