affected functions in the migration from addr:port to nickname for ORs

        o Move (most of) the router/directory code out of main.c

Mid-term:

        . migrate to using nickname rather than addr:port for routers

                o decide_aci_type

                - generate onion skins

                  - circuit_send_next_onion_skin

                  - circuit_extend

                  - onion_generate_cpath

                - get_unique_aci_by_addr_port

                - circ->n_addr and circ->n_port

                  - circuit_enumerate_by_naddr_nport

                - cpath layers

                - connection_or_connect

                - connection_exact_get_by_addr_port

                - connection_twin_get_by_addr_port

                - router_get_by_addr_port

                - connection_or_init_conn_from_router

                - tag_pack, tag_unpack, connection_cpu_process_inbuf

                - directory_initiate_command

        . Redo scheduler

                o fix SSL_read bug for buffered records

                - make round-robining more fair