doc: mfcalc: demonstrate %printer.

* doc/bison.texinfo (Printer Decl): New.
Number mfcalc.y snippets so that they are output in
the proper order.
(The mfcalc Main): Use yydebug.
(Debugging): Simplify the text.
(Enabling Traces, Mfcalc Traces, The YYPRINT Macro): New.
(Table of Symbols): Document YYPRINT and YYFPRINTF.

(cherry picked from commit 93c150b666c3345bdd1527a5495a4787d8c3b5bf)

Conflicts:

	doc/bison.texinfo