New CANVAS Demo, updated PNG Viewer Demo

Demo_Canvas.py

@@ -0,0 +1,22 @@
+import PySimpleGUI as gui
+
+canvas = gui.Canvas(size=(100,100), background_color='red')
+
+layout = [
+           [canvas],
+           [gui.T('Change circle color to:'), gui.ReadFormButton('Red'), gui.ReadFormButton('Blue')]
+           ]
+
+form = gui.FlexForm('Canvas test')
+form.Layout(layout)
+form.ReadNonBlocking()
+
+cir = canvas.TKCanvas.create_oval(50, 50, 100, 100)
+
+while True:
+    button, values = form.Read()
+    if button is None: break
+    if button is 'Blue':
+        canvas.TKCanvas.itemconfig(cir, fill = "Blue")
+    elif button is 'Red':
+        canvas.TKCanvas.itemconfig(cir, fill = "Red")