Made acceptableOverheadRatio configurable
Added bulk get to AbstractAppendingLongBuffer classes, for faster retrieval.
Introduced a new variant, AppendingPackedLongBuffer which solely relies on PackedInts as a back-end. This new class is useful where people have non-negative numbers with a fairly uniform distribution over a fixed (limited) range. Ex. facets ordinals.
To distinguish it from AppendingPackedLongBuffer, delta based AppendingLongBuffer was renamed to AppendingDeltaPackedLongBuffer
Fixed an Issue with NullReader where it didn't respect it's valueCount in bulk gets.