Create Tailwind module

Moving the UI.tw function into Tailwind.use. Creating and consuming some
functions like Tailwind.if_ and Tailwind.when to make it easier to conditionally
style some of my components.

website/sandbox/learnpianochords/src/Tailwind.elm

@@ -0,0 +1,29 @@
+module Tailwind exposing (..)
+
+{-| Functions to make Tailwind development in Elm even more pleasant.
+-}
+
+
+{-| Conditionally use `class` selection when `condition` is true.
+-}
+when : Bool -> String -> String
+when condition class =
+    if condition then
+        class
+
+    else
+        ""
+
+
+if_ : Bool -> String -> String -> String
+if_ condition whenTrue whenFalse =
+    if condition then
+        whenTrue
+
+    else
+        whenFalse
+
+
+use : List String -> String
+use styles =
+    String.join " " styles