refactor: add display.Pin interface and use it everywhere that is easy to do so

Signed-off-by: deadprogram <ron@hybridgroup.com>

pin.go

@@ -0,0 +1,10 @@
+package drivers
+
+// Pin is a digital pin interface. It is notably implemented by the
+// machine.Pin type.
+type Pin interface {
+	Get() bool
+	High()
+	Low()
+	Set(high bool)
+}