Change the handling of the symbols in the skeletons.

Before we were using tables which lines were the symbols and which
columns were things like number, tag, type-name etc.  It is was
difficult to extend: each time a column was added, all the numbers had
to be updated (you asked for colon $2, not for "tag").  Also, it was
hard to filter these tables when only a subset of the symbols (say the
tokens, or the nterms, or the tokens that have and external number
*and* a type-name) was of interest.

Now instead of monolithic tables, we define one macro per cell.  For
instance "b4_symbol(0, tag)" is a macro name which contents is
self-decriptive.  The macro "b4_symbol" provides easier access to
these cells.

	* src/output.c (type_names_output): Remove.
	(symbol_numbers_output, symbol_definitions_output): New.
	(muscles_output): Call them.
	(prepare_symbols): Define b4_symbols_number.