HTML-like multipart/form-data POST file upload for Net::HTTP (rfc1867)

Hi people. I think this has been solved a hundred times in lots of
different places, but never working together with Net::HTTP, and never
as a separate general library (if I’m wrong —sorry, library authors, I
didn’t find yours!). So I created “multipart”: a ruby gem that
extends Net::HTTP::Post with a method to format file upload parameters
as multipart/form-data, per rfc1867. It supports multiple file
parameters per request, and also multiple files per parameter
(multipart/mixed). All you gotta do is gem install multipart and read
the rdocs.

It’s in beta and by that I mean UNTESTED. Before doing anything
serious, help me debug it :wink: