doc: lalr1.cc and variants.

doc: lalr1.cc and variants.

	* doc/bison.texinfo (Decl Summary): Document the "lex_symbol" and
	"variant" %define variables.
	(C++ Semantic Values): Split into...
	(C++ Unions, C++ Variants): these.
	The latter is new.
	(C++ Parser Interface): Fix type names.
	Document parser::syntax_error.
	Document the fact that locations are not mandatory.
	(C++ Scanner Interface): Split into...
	(Split Symbols, Complete Symbols): these.
	The later is new.
	(Calc++ Parsing Driver): Use variants.
	Add more comments.
	Adjust style.
	(Calc++ Parser): Declare all the tokens, no
	longer accept raw characters.
	Remove %union.
	Adjust types and printers.
	Remove destructors.
	(Calc++ Scanner): Use make_<SYMBOL> functions.
	Use strerror in error message.