ParallelUserAgent (or PUA for short) is an extension of the existing libwww-5.x
distribution. It allows you to connect to download several Web pages in
_parallel_, without having to request each page one after the other.

Instead of retrieving each single page using LWP::UserAgent::request or
::simple_request methods, you first "register" all pages that you wish to
download in parallel and then call PUA's "wait" method, which will then make all
the necessary connections and download the pages.

You can define callback routines which will be called whenever a connection is
established, is cut off, new data comes in or a request finishes. The
subroutines can be global for all requests you registered, or different for
every single request.

Callbacks for example allow you to print status updates as the responses come
in, or even immediately post follow-up requests based on the responses, all
within the same single "wait" cycle.
