This will make it possible for clients to instruct the user when they need to rebuild the index.
This significantly speeds up the case where you need a count for a single term or single label.
Right now these simple add a count in addition to an offset within the postings list. In the future, this change will enable: a) quick results for counts of simple (single-term or single-label) queries, which actually is a common use case b) a much more space-efficient postings structure; and c) much quicker, skiplist-style queries for phrases (which right now are pretty slow). Bump the segment version number to account for this.
I.e. even if you use Query#or, #and or #term_map, still provide a @query on the result.