- Disallow some illegal expressions.
- Fix chained print expressions.
This causes 10 first/follow conflicts, where I'm not sure how
to solve them or if that would even be feasible to do. Example:
<? print 1 || print 2 || print 3; ?>
php-parser handles this correctly, but conceptually it wouldn't
know if the second || belongs to the first booleanOrExpression or
is a new booleanOrExpression below the assignmentExpression of the