Add MaxFreq and MinFreq filters
Add tests for MinFrequencyFilter over disjunction and multiterm
Remove FieldedQuery class

Instead, we add .getField() directly to Query, which will return the field (if
valid for the query) or null if the query spans multiple fields.
Add test for cross-field frequency queries
Make highlighter tests compile
Change release version to r1581360-intervals-1.3.1-SNAPSHOT

We've changed the API, so let's change the version...
Improve toString() for IntervalFilterQuery