parsergen: implement new handling of IN/OUT and NEWLINE

IN/OUT are now expected in the grammar.
In a state where an IN can be shifted, IN symbols are significant to the
grammar.  IN symbols appearing anywhere else are ignored (except for how
they affect NEWLINEs).

OUT symbols are ignored precisely when the matching IN was ignored.

NEWLINEs are ignored if the most recent IN was ignored, otherwise they
are significant for the grammar.

Signed-off-by: NeilBrown <neil@brown.name>