Make bit_vector msgpack-serializable
Use bit_table_t as the diff type of bit_index_storage
Remove private redefinition of lsh_table_t
Remove old TODO comment
Let diff type in portable_mixer variable
Change diff type of lsh_index_storage from string to lsh_master_table_t
Include inverted_index_storage.hpp directly instead of recommender_storage.hpp
Remove recommender_storage_base
Remove recommender_storage.hpp