Grammar rules in Contributor Guide summary are fragmented

[Robin Bannister]

Hallo,


The Contributor Guide appendix 'LilyPond grammar' displays a summary 
(ly-grammar.txt) which is derived from a summary produced by bison.

In the first section a production rule has a label on the left which 
introduces the alternatives listed on the right. Or rather, _most_ rules 
are like that, but for a few of them the label occurs twice. So if you 
are looking for a rule and find it, you may overlook some of its 
alternatives.

This is OK by bison (and maybe a practised eye) but not by me.
So I propose a readability enhancement where there is only one label per 
rule and submit a revised yyout2grammar.py which caters for this.

While testing it I noticed and corrected several errors:
  - the elimination of @-items in the alternatives is inaccurate
  - in the second section, continuation lines pile up at the top
  - in the third section, more than 30 nonterminals are missing and
    @-rules are included

In the script, the production rule part is completely rewritten and the
rest is extensively refactored. See yyout2g_robin_A.py

I worked with bison-2.4.1 (GnuWin32) and obtained parser.yy and 
yyout2grammar.py from git a few days ago, i.e post 2.19.80.
The following summaries are generated from that snapshot:
  - before: ly-grammar.txt
  - after:  ly-g_robin_A.txt


  Cheers,
  Robin

ly-grammar.txt
Description: Text document

ly-g_robin_A.txt
Description: Text document

yyout2g_robin_A.py.txt
Description: Text document