Fix for Issue # 20

[ultrasuperpingu]

Fix for issue #20 (c# only for now)

The grammar provided in the issue is now correctly parsed. But the following grammar will not :

EOF -> @"^$";
[Skip] WHITESPACE -> @"\s+";
LIST -> "LIST";
END -> "END";
IDENTIFIER -> @"[a-zA-Z_][a-zA-Z0-9_]*";
Expr -> LIST IdList END;

IdList -> IDENTIFIER+;
Start -> (Expr)+ EOF;

But TinyPG is a LL(1) parser, not able to parse many grammars so it seems to me a good compromise (between the actual code and removing Partial Context Sensitive/Ambiguous Grammars feature).