Reconstruct the record of peers.

Add an dynamic array to record the available peers. Add a zhash_t field to record all information of peers.
Optimise the dz_broker's mainloop

Read all of the sockets that have revents set after zmq_poll() return;
Use zmsg_recv_nowait() when handling localbe and localfe and keep calling zmsg_recv_nowait() until receiving NULL
remove hiredis client
change handwritten Makefile to CMake tool