Add benchmarking for bitmaps

Here are the results on my laptop:
```
BitmapCreationBenchmark.testRandomAddition[0]: [measured 10 out of 20 rounds, threads: 1 (sequential)]
 round: 0.49 [+- 0.07], round.block: 0.00 [+- 0.00], round.gc: 0.00 [+- 0.00], GC.calls: 16, GC.time: 0.01, time.total: 9.91, time.warmup: 5.06, time.bench: 4.86
BitmapCreationBenchmark.testLinearAdditionDescending[0]: [measured 1000 out of 1010 rounds, threads: 1 (sequential)]
 round: 0.01 [+- 0.00], round.block: 0.00 [+- 0.00], round.gc: 0.00 [+- 0.00], GC.calls: 74, GC.time: 0.03, time.total: 5.82, time.warmup: 0.06, time.bench: 5.76
BitmapCreationBenchmark.testToImmutableByteArray[0]: [measured 1000 out of 1010 rounds, threads: 1 (sequential)]
 round: 0.00 [+- 0.00], round.block: 0.00 [+- 0.00], round.gc: 0.00 [+- 0.00], GC.calls: 0, GC.time: 0.00, time.total: 1.80, time.warmup: 0.02, time.bench: 1.78
BitmapCreationBenchmark.testRandomAddition[1]: [measured 10 out of 20 rounds, threads: 1 (sequential)]
 round: 0.00 [+- 0.00], round.block: 0.00 [+- 0.00], round.gc: 0.00 [+- 0.00], GC.calls: 0, GC.time: 0.00, time.total: 0.12, time.warmup: 0.08, time.bench: 0.04
BitmapCreationBenchmark.testLinearAdditionDescending[1]: [measured 1000 out of 1010 rounds, threads: 1 (sequential)]
 round: 0.00 [+- 0.00], round.block: 0.00 [+- 0.00], round.gc: 0.00 [+- 0.00], GC.calls: 10, GC.time: 0.01, time.total: 4.26, time.warmup: 0.04, time.bench: 4.22
BitmapCreationBenchmark.testToImmutableByteArray[1]: [measured 1000 out of 1010 rounds, threads: 1 (sequential)]
 round: 0.01 [+- 0.00], round.block: 0.00 [+- 0.00], round.gc: 0.00 [+- 0.00], GC.calls: 27, GC.time: 0.01, time.total: 5.11, time.warmup: 0.05, time.bench: 5.06
BitmapCreationBenchmark.testLinearAddition[0]: [measured 1000 out of 1010 rounds, threads: 1 (sequential)]
 round: 0.00 [+- 0.00], round.block: 0.00 [+- 0.00], round.gc: 0.00 [+- 0.00], GC.calls: 0, GC.time: 0.00, time.total: 3.48, time.warmup: 0.04, time.bench: 3.45
BitmapCreationBenchmark.testLinearAddition[1]: [measured 1000 out of 1010 rounds, threads: 1 (sequential)]
 round: 0.00 [+- 0.00], round.block: 0.00 [+- 0.00], round.gc: 0.00 [+- 0.00], GC.calls: 9, GC.time: 0.00, time.total: 2.95, time.warmup: 0.03, time.bench: 2.92
2014-11-13 12:47:23,995 INFO [main] io.druid.segment.data.BitmapCreationBenchmark - Entry [0] is io.druid.segment.data.ConciseBitmapSerdeFactory
2014-11-13 12:47:23,995 INFO [main] io.druid.segment.data.BitmapCreationBenchmark - Entry [1] is io.druid.segment.data.RoaringBitmapSerdeFactory
```