Better parsing of statement lists

These commits fix the issue described in #7.
It was a real pain to modify this grammar correctly, but I finally managed to get a grammar with even less shift/reduce conflicts as before :)
If this flag is set, the parser will trace what kind of shifts and reductions it performs.
When I tried different ways of writing this grammar, it turned out to be very useful for understanding the problems my grammar had while I debugged my tests.