Fix #104: Add support for the attachment API.

[n1k0]

WiP, refs #104, cc @leplatrem.

I'm stuck here with this kinto server error Kinto/kinto-attachment#100

It's certainly a problem with the patch implementation as attaching a file using httpie and the kinto admin both work just fine. It may be related to jsdom's FormData implementation.

I'd be happy to get some help here.

[leplatrem]

Yes, it is combination of isomorphic-fetch and jsdom FormData I guess.
The header Content-Type is not sent with multipart automatically, and from the server side the body appears empty.

In the examples given on node-fetch they use the form-data package

// post with form-data (detect multipart)

var FormData = require('form-data');
var form = new FormData();
form.append('a', 1);
fetch('http://httpbin.org/post', { method: 'POST', body: form })
    .then(function(res) {
        return res.json();
    }).then(function(json) {
        console.log(json);
    });

I pushed a very dirty commit on the branch with some code that works... let's say it's step 1, but it introduces some ugly dependencies to form-data package and node Buffer (whose browserify counterpart is huge), just to run the tests :)

[leplatrem]

Made something slightly better...

[leplatrem]

TODO: add @capable decorator