Emacs Lisp manual updates.

Emacs Lisp manual updates.

* doc/lispref/intro.texi (A Sample Function Description): Special notation
used for macros too.

* doc/lispref/objects.texi (Ctl-Char Syntax, Other Char Bits): Copyedits.
(Symbol Type): Add xref for keyword symbols.
(Sequence Type): Clarify differences between sequence types.
(Cons Cell Type): Add "linked list" index entry.
(Non-ASCII in Strings): Copyedits.
(Equality Predicates): Symbols with same name need not be eq.

* doc/lispref/numbers.texi (Float Basics): Document isnan, copysign, frexp and
ldexp.  Move float-e and float-pi to Math Functions node.