4.0.0

A lot has happened since 3.0.0! The API is smaller, and more focused and I'm
excited about that. In particular, BodyReader and its friends have been
removed. Since this is the official upgrade for Elm 0.18, the new
elm-lang/http package has a lot of influence. The new Http package includes
a much more cohesive experience for declaring expectations of response bodies.
See the Http.Expect type in elm-lang/http.
This feature is even reminiscent of BodyReader!

Since we have this as a part of the platform now, all of the BodyReader-
related features are gone. For these you'll just "use the platform", as they
say, and make use of withExpect in your builder pipelines. In the future
we may include fancier, custom Expect formulations for your convenience.

Secondly, you'll now have the option to convert a RequestBuilder a into an
Http.Request a or send it directly using HttpBuilder.send, which has the
same signature as Http.send. This helps to keep your builder pipelines clean
while also leaving you the option to get out an Http.Request if you need.

Long story short, HttpBuilder is just about building requests, just like
when it started out. The platform covers the rest.

Here's the list of all changes:

Removals

• url: use withQueryParams instead to add query params to your url
• withBody: use one of the more specific with*Body functions instead
• withMultipartBody: string multipart bodies are the only type supported by
  elm-lang/http currently, sojust use withMultipartStringBody instead
• withMimeType: the first parameter to withStringBody will set your MIME
  type automatically. Alternatively, set a header with withHeader
• withCacheBuster: since we're giving up control of the send process, we can't
  chain on a Task to get the current time
• withZeroStatusAllowed: we don't control the send process. You can handle
  this yourself under the Http.BadStatus error when you deal with errors in
  your send msg tagger.
• BodyReader: see intro
• stringReader: see intro
• jsonReader: see intro
• unitReader: see intro
• Error: since we don't control the send process we don't need this
• Response: same as Error
• toSettings: Http.Settings doesn't exist anymore, it was moved under
  Http.Request
• Request: since we expect you'll need to import Http now anyway, you can
  just import this from Http
• Settings: see toSettings

Breaking Changes

• RequestBuilder -> RequestBuilder a, where the type parameter is the
  expected type of the returned payload.
• get, post, etc. return RequestBuilder (). The default is to make no
  attempt to decode anything, so it is (). You can use withExpect to attach
  an Http.Expect MyType, which will turn it into a RequestBuilder MyType.
• toRequest returns an Http.Request a
• send wraps Http.send, read up on it to see how it works.

Additions

• withExpect: attach an Http.Expect to the request
• withQueryParams: decorate the URL with query params

A sincere thank you to @evancz, @rtfeldman, @Bogdanp, and @knewter for time and
discussions that helped me make the decisions that led to these changes!

And a shoutout to @prikhi for taking the time to update the existing API for
0.18 and publishing it as priki/elm-http-builder.