Updates to Font Lock docs in Lisp manual.

Updates to Font Lock docs in Lisp manual.

* doc/lispref/modes.texi (Minor Modes): Update how mode commands should treat
arguments now.
(Mode Line Basics): Clarify force-mode-line-update.
(Mode Line Top): Note that the example is not realistic.
(Mode Line Variables, Mode Line Data, %-Constructs, Header Lines)
(Emulating Mode Line): Use "mode line" instead of "mode-line", and
"mode line construct" instead of "mode line specification".
(Syntactic Font Lock): Remove mention of obsolete variable
font-lock-syntactic-keywords.
(Setting Syntax Properties): Node deleted.
(Font Lock Mode): Note that Font Lock mode is a minor mode.
(Font Lock Basics): Note that syntactic fontification falls back
on `syntax-table'.
(Search-based Fontification): Emphasize that font-lock-keywords
should not be set directly.
(Faces for Font Lock): Avoid some confusing terminology.
(Syntactic Font Lock): Minor clarifications.