Replace Milkis with Affjax (#4)

* It builds

* Removed typoed duplicate import

* Pass the method to Affjax

* Use record destructuring for request properties

* Requests can be built safely now that Milkis is removed

* Removed client/server separation and expanded main exports

Merge pull request #3 from jonasbuntinx/master

Added status 422 Unprocessable Entity

Moved the helper to the main project, since it didn't fit here