Consolidate Plug Locations (#146)

Move these two plugs with their other friends.

Note that this commit introduces a backwards incompatible change: it
renames the `PlugResponseContentType` to `ResponseContentType`.

lib/jsonapi/plug.ex → lib/jsonapi/plugs/response_content_type.ex

@@ -1,4 +1,4 @@
-defmodule JSONAPI.PlugResponseContentType do
+defmodule JSONAPI.ResponseContentType do
   @moduledoc """
   Simply add this plug to your endpoint or your router :api pipeline and it will
   ensure you return the correct response type.

test/jsonapi/plugs/response_content_type_test.exs

@@ -0,0 +1,27 @@
+defmodule JSONAPI.ResponseContentTypeTest do
+  use ExUnit.Case
+  use Plug.Test
+
+  alias JSONAPI.ResponseContentType
+
+  test "sets response content type" do
+    conn =
+      :get
+      |> conn("/example", "")
+      |> ResponseContentType.call([])
+      |> send_resp(200, "done")
+
+    assert get_resp_header(conn, "content-type") == ["application/vnd.api+json; charset=utf-8"]
+  end
+
+  test "can be overridden when in play" do
+    conn =
+      :get
+      |> conn("/example", "")
+      |> Plug.Conn.assign(:override_jsonapi, true)
+      |> ResponseContentType.call([])
+      |> send_resp(200, "done")
+
+    refute get_resp_header(conn, "content-type") == ["application/vnd.api+json; charset=utf-8"]
+  end
+end