widget,widget/material: export CheckBox.Checked

Similar to the previous change to Enum, expose the current state of
the CheckBox. Rename the Checked method to just Update and get rid
of the SetChecked method.

Fixes gio#100

Signed-off-by: Elias Naur <mail@eliasnaur.com>

widget/checkbox.go

@@ -6,22 +6,19 @@ import (
 )
 
 type CheckBox struct {
-	click   gesture.Click
-	checked bool
+	Checked bool
+
+	click gesture.Click
 }
 
-func (c *CheckBox) SetChecked(value bool) {
-	c.checked = value
-}
-
-func (c *CheckBox) Checked(gtx *layout.Context) bool {
+// Update the checked state according to incoming events.
+func (c *CheckBox) Update(gtx *layout.Context) {
 	for _, e := range c.click.Events(gtx) {
 		switch e.Type {
 		case gesture.TypeClick:
-			c.checked = !c.checked
+			c.Checked = !c.Checked
 		}
 	}
-	return c.checked
 }
 
 func (c *CheckBox) Layout(gtx *layout.Context) {