A mode where tag order actually matters. --ordered currently doesn't do much.

Options and rule flags Ordered/Unordered to change the mode for whole grammar/rules.

Opt-in for composite tags with placeholders:

• _ a single tag
• + one-or-more tags
• * zero-or-more tags

If a composite tag has any of the placeholders, it opts in to ordered consecutive mode. Maybe have options and rule flags for forcing consecutive on all tags.

See also #42