fixes #475 Hash table does not decrease size
fixes #475 Hash table does not decrease size

nn_hash.items will increase by nn_hash_insert but won't decrease

JackDunaway/featherweight-nanomsg,zerotacg/nanomsg,imp/nanomsg,thisco-de/nanomsg,reqshark/nanomsg,snikulov/nanomsg,thisco-de/nanomsg,zerotacg/nanomsg,imp/nanomsg,wirebirdlabs/featherweight-nanomsg,yan97ao/nanomsg,yan97ao/nanomsg,JackDunaway/featherweight-nanomsg,JackDunaway/featherweight-nanomsg,featherweight/ftw-kernel-nanomsg,snikulov/nanomsg,wirebirdlabs/featherweight-nanomsg,zerotacg/nanomsg,imp/nanomsg,yan97ao/nanomsg,wirebirdlabs/featherweight-nanomsg,featherweight/ftw-kernel-nanomsg,reqshark/nanomsg,reqshark/nanomsg