Support "in" operator in grammar

Support "in" operator in grammar

This changes the previous comparison operations from being marked
as solely comparion expressions and expands them out to be generation
operator expressions. This allows us to easily support the "in"
operator, which in the current Jinja parser is handled exactly the
same as the other operations, but it does require us to special case
the automated conversion of the "not ... in" expression to a "notin"
expression.