widget: rename CheckBox to Bool

We're about to introduce the Switch widget that re-uses the same
state type as CheckBox. The Bool name covers both uses.

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

widget/bool.go

@@ -0,0 +1,26 @@
+package widget
+
+import (
+	"gioui.org/gesture"
+	"gioui.org/layout"
+)
+
+type Bool struct {
+	Value bool
+
+	click gesture.Click
+}
+
+// Update the checked state according to incoming events.
+func (b *Bool) Update(gtx *layout.Context) {
+	for _, e := range b.click.Events(gtx) {
+		switch e.Type {
+		case gesture.TypeClick:
+			b.Value = !b.Value
+		}
+	}
+}
+
+func (b *Bool) Layout(gtx *layout.Context) {
+	b.click.Add(gtx.Ops)
+}