Add an atomic Boolean type (#4)

* Add an atomic Boolean type

Fixes #2.

* Feedback from CR

- Rename Swap to Toggle
- Add a more Swap-like Swap

* Add boolToInt helper

stress_test.go

@@ -103,3 +103,20 @@ func TestStressUint64(t *testing.T) {
 		}()
 	}
 }
+
+func TestStressBool(t *testing.T) {
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(_parallelism))
+	atom := NewBool(false)
+	for i := 0; i < _parallelism; i++ {
+		go func() {
+			for j := 0; j < _iterations; j++ {
+				atom.Load()
+				atom.Store(false)
+				atom.Swap(true)
+				atom.Load()
+				atom.Toggle()
+				atom.Toggle()
+			}
+		}()
+	}
+}