: head( path, header = nil )
    о path ˤ륨ƥƥΥإåΤߤޤ
    ޤ header  nil ǤʤХꥯȤȤˤƤ
    HTTP إåȤƽ񤭤ߤޤheader ϥϥåǡ
    ֥إå̾ => ơפΤ褦ʷǤʤФޤ

    HTTPResponse ֥Ȥ֤ޤ

    1.1 Ǥ 3xx (ƻԲǽʥ顼)ФƤ㳰ȯޤξ
    HTTPResponse 㳰֥Ȥ err.response 뤳ȤǤޤ
     1.2 Ǥ㳰ȯޤ

        response = nil
        Net::HTTP.start( 'some.www.server', 80 ) {|http|
            response = http.head( '/index.html' )
        }
        p response['content-type']

