Update to airbase 0.21-SNAPSHOT
Simplify SortedRangeSet.Builder and add benchmark

Collect ranges and do one pass at the end to merge adjacent and overlapping ranges.

This improves performance for this class by about 6x for a synthetic benchmark with 10000 ranges

        Benchmark                                            Mode   Samples   Mean  Mean error   Units
Before: c.f.p.s.BenchmarkSortedRangeSet.benchmarkBuilder     avgt        10  5.416       0.150   ms/op
After:  c.f.p.s.BenchmarkSortedRangeSet.benchmarkBuilder     avgt        10  0.867       0.016   ms/op