add Z version of Button example

Button/Z/button.json

+{
+  "svg": "../button.svg",
+  "items": [
+    {
+      "id": "button",
+      "attr": "fill",
+      "value": "IF button=True THEN \"green\" ELSE \"red\" END"
+    },
+    {
+      "id": "button",
+      "attr": "stroke-width",
+      "value": "IF ENABLED(\"pressButton\") THEN 6 ELSE 1 END",
+      "ignore": "is now used in hover below"
+    },
+    {
+      "id": "button_%0",
+      "attr": "visibility",
+      "value": "\"hidden\"",
+      "repeat": [ "TRUE", "FALSE" ]
+    }
+  ],
+  "events": [
+    {
+      "id": "button",
+      "event": "toggleButton",
+      "hovers": [{ "attr":"stroke-width", "enter":"6", "leave":"1"},
+                 { "attr":"opacity", "enter":"0.8", "leave":"1.0"}]
+    }
+  ]
+}

Button/Z/button.tex

+\documentclass[a4paper]{article}
+\usepackage{fuzz}
+
+\begin{document}
+
+
+\section*{Button}
+\subsection*{Data types}
+We define the type for booleans:
+\begin{zed}
+  Bool ::= True | False\\
+\end{zed}
+
+\subsection*{State}
+The current state of the button is a boolean
+\begin{schema}{State}
+	button: Bool
+\end{schema}
+
+
+\subsection*{Operations}
+
+\begin{schema}{pressButton}
+	\Delta State
+\where
+	button = False\\
+	button' = True
+\end{schema}
+
+\begin{schema}{toggleButton}
+	\Delta State
+\where
+	button' = (\IF button= True \THEN False \ELSE True) 
+\end{schema}
+
+\begin{schema}{Init}
+    State\\
+  \where
+   button = False
+ \end{schema}
+
+\end{document}