--- Resolv.getaddress(name)
--- Resolv.getaddresses(name)
--- Resolv.each_address(name) {|address| ...}
    They lookups IP addresses of name which represents a hostname
    as a string.

    getaddress returns first entry of lookupped addresses.
    getaddresses returns lookupped addresses.
    each_address iterates over lookupped addresses.

    :
      Resolv.getaddress("www.ruby-lang.org").to_s #=> "210.251.121.214"

