Log Message:
Update ruby-httpclient to 2.2.2.
While here, install document again.

== Changes

= Changes in 2.2.2 =

  Oct 17, 2011 - version 2.2.2

    * Bug fixes

      * Do not sort query params on request: Wrongly sorted query params for
        easier debugging but the order of request parameter should be
        preserved. #65

    * Changes

      * Set responce String encoding if possible.  Parse content-type response
        header with some helps from OpenURI::Meta and set response String
        encoding. #26

      * Improve connection cache strategy.  Reuse cached session in MRU order,
        not in LRU.  MRU is more server friendly than LRU because it reduces
        number of cached sessions when a number of requests drops after an
        usaage spike.

        With reusing sessions in LRU order, all sessions are equally checked if
        it's closed or not, as far as there's a request to the same site.  With
        reusing sessions in MRU order, old cold sessions are kept in cache long
        time even if there's a request to the same site.  To avoid this leakage,
        this version adds keep_alive_timeout property and let SessionManager
        scrub all sessions with checking the timeout for each session.  When the
        session expires against the last used time, it's closed and collected.

        keep_alive_timeout is 15[sec] by default. The value is from the default
        value for KeepAliveTimeout of Apache httpd 2.  #68 #69