Add fullscreen requesting for windows

ui/canvas.go

@@ -3,6 +3,7 @@ package ui
 // Canvas defines a graphical canvas to which a CanvasObject or Container can be added.
 // Each canvas has a scale which is automatically applied during the render process.
 type Canvas interface {
+	Content() CanvasObject
 	SetContent(CanvasObject)
 	Refresh(CanvasObject)
 	Contains(CanvasObject) bool

ui/window.go

@@ -9,6 +9,13 @@ type Window interface {
 	Title() string
 	// SetTitle updates the current title of the window
 	SetTitle(string)
+
+	// Fullscreen returns whether or not this window is currently full screen
+	Fullscreen() bool
+	// SetFullscreen changes the requested fullscreen property
+	// true for a fullscreen window and false to unset this.
+	SetFullscreen(bool)
+
 	// Show the window on screen
 	Show()
 	// Hide the window from the user.