ChunkManager optimize chunks handling in small and big worlds
Small worlds gets benefits with using int-object map instead long-object (in area -32768...32767 by x and z)
Large worlds gets benefits by using efficient map by Colt project, which a little (3-6%) slower in writing, but greatly faster
(400-500% from Java's HashMap and 150-180% from Trove's maps) on reading.
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