feature: server now can bind with bind_host and bind_sock

bind_host: string of hostname to listen on.
bind_sock: unix sock file path to listen on, and when this is present, bind_host/bind_port will have no effect.

fix: when server merge the conf and user's customization, make it a copy
Merge pull request #19 from liyu1981/dev

feature: server now can bind with bind_host and bind_sock