Create a diagram of a binary tree.
Example tree:
Node 2 (Node 1 Empty Empty) (Node 3 Empty Empty)
The arguments are value, leftTree, rightTree.
diagramView : (v -> String) -> (v -> String) -> BinaryTree v -> Html msg
Pass in functions to set the color and text.
diagramView (\v -> v.color) (\v -> v.text) tree
diagramView (\_ -> "blue") (\_ -> "") tree