Add multipart/form-data support

[ixti]

Resolves #73

[sferik]

@ixti Am I missing something? Where is HTTP::FormData::File defined?

[ixti]

@sferik it's not ready yet - work in progress :D

[ixti]

@sferik pushed a patch with api draft. With 99% confidence it will stay as it is -- only internals will be implemented properly. FormData::File might get splitted into IO and File actually.

[ixti]

Finally! I've did it!!! :D

Moved FormData code into separate gem: https://github.com/ixti/form_data.rb

# Usage inside with HTTP Gem:

HTTP.post(some_url, :form => {
  :username => "ixti",
  :avatar => FormData::File.new("/path/to/file.jpg"),
  :cv => FormData::File.new(io, :filename => "cv.pdf")
})

# Standalone usage:

form = FormData.create({
  :username => "ixti",
  :avatar => FormData::File.new("/path/to/file.jpg"),
  :cv => FormData::File.new(io, :filename => "cv.pdf")
})

@sferik, @tarcieri I have avoided HTTP namespace mostly to shorten File constructor. Although I'm OK to rename gem to be http-form_data or whaever and include HTTP namespace: really don't know what will be better as it is now or with namespace.

[ixti]

Notice that form_data is pretty simple right now. In future versions I hope to implement streaming, so that sending files to socket will become possible without prior reading it completely. Also I want to support nested hashes, so that:

FormData.create({
  :foo => { :bar => "baz" }
}).to_s
# => foo[bar]=baz

FormData.create({
  :foo => { :bar => "baz" },
  :img => FormData::File.new("/home/ixti/avatar.png")
}).to_s
# =>
# --boundary
# Content-Disposition: form-data; name="foo[bar]"
#
# baz
# --boundary
# Content-Disposition: form-data; name="img"; filename="avatar.png"
# Content-Type: application/octet-stream
#
# ...
# --boundary--

[tarcieri]

LGTM 👍