multipart form post accessory for Net::HTTP

 Adds a streamy multipart form post capability to Net::HTTP. Also
 supports other methods besides POST.
 .
 FEATURES/PROBLEMS:
 .
  * Appears to actually work. A good feature to have.
  * Encapsulates posting of file/binary parts and name/value parameter parts,
    similar to most browsers' file upload forms.
  * Provides an UploadIO helper class to prepare IO objects for inclusion in
    the params hash of the multipart post object