Re-add part3

advanced/part3/src/Loading.elm

@@ -0,0 +1,25 @@
+module Loading exposing (error, icon, slowThreshold)
+
+{-| A loading spinner icon.
+-}
+
+import Asset
+import Html exposing (Attribute, Html)
+import Html.Attributes exposing (alt, height, src, width)
+import Process
+import Task exposing (Task)
+
+
+icon : Html msg
+icon =
+    Html.img [ Asset.src Asset.loading, width 64, height 64, alt "Loading..." ] []
+
+
+error : String -> Html msg
+error str =
+    Html.text ("Error loading " ++ str ++ ".")
+
+
+slowThreshold : Task x ()
+slowThreshold =
+    Process.sleep 500