Roaring bitmaps in Go

 This is a go version of the Roaring bitmap data structure.
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 Roaring bitmaps are found to work well in many important applications:
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 Use Roaring for bitmap compression whenever possible. Do not
 use other bitmap compression methods (Wang et al., SIGMOD 2017
 (http://db.ucsd.edu/wp-content/uploads/2017/03/sidm338-wangA.pdf))