v0.5.2

• Optimize performance of some functions through deferred deserialization
  Optimized functions include rb_or_cardinality,rb_and,rb_and_cardinality,rb_andnot,rb_andnot_cardinality,rb_xor_cardinality,rb_cardinality,rb_is_empty,rb_exsit,rb_equals,rb_not_equals,rb_intersect,rb_contains,rb_containedby,rb_jaccard_dist,rb_min,rb_max,rb_rank,rb_index

  for detail please refer to https://github.com/ChenHuajun/pg_roaringbitmap/wiki/Performance-optimization-by-deferred-deserialization

• Upgrade CRoaring to v0.2.66

• add benchmark script

• add travis CI support