joystick: provide constant values for existing joystick configurations

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

examples/joystick_ps3.go

@@ -13,7 +13,7 @@ import (
 
 func main() {
 	joystickAdaptor := joystick.NewAdaptor()
-	stick := joystick.NewDriver(joystickAdaptor, "dualshock3")
+	stick := joystick.NewDriver(joystickAdaptor, joystick.Dualshock3)
 
 	work := func() {
 		// buttons

examples/joystick_ps4.go

@@ -13,7 +13,7 @@ import (
 
 func main() {
 	joystickAdaptor := joystick.NewAdaptor()
-	stick := joystick.NewDriver(joystickAdaptor, "dualshock4")
+	stick := joystick.NewDriver(joystickAdaptor, joystick.Dualshock4)
 
 	work := func() {
 		stick.On(joystick.SquarePress, func(data interface{}) {

examples/joystick_xbox360.go

@@ -13,7 +13,7 @@ import (
 
 func main() {
 	joystickAdaptor := joystick.NewAdaptor()
-	stick := joystick.NewDriver(joystickAdaptor, "xbox360")
+	stick := joystick.NewDriver(joystickAdaptor, joystick.Xbox360)
 
 	work := func() {
 		stick.On(joystick.APress, func(data interface{}) {

examples/joystick_xbox360_rock_band_drums.go

@@ -13,7 +13,7 @@ import (
 
 func main() {
 	joystickAdaptor := joystick.NewAdaptor()
-	stick := joystick.NewDriver(joystickAdaptor, "xbox360RockBandDrums")
+	stick := joystick.NewDriver(joystickAdaptor, joystick.Xbox360RockBandDrums)
 
 	work := func() {
 		stick.On(joystick.RedPress, func(data interface{}) {

platforms/joystick/joystick_driver.go

@@ -10,6 +10,23 @@ import (
 	"gobot.io/x/gobot"
 )
 
+const (
+	// Dualshock3 joystick configuration.
+	Dualshock3 = "dualshock3"
+
+	// Dualshock4 joystick configuration.
+	Dualshock4 = "dualshock4"
+
+	// TFlightHotasX flight stick configuration.
+	TFlightHotasX = "tflightHotasX"
+
+	// Xbox360 joystick configuration.
+	Xbox360 = "xbox360"
+
+	// Xbox360RockBandDrums controller configuration.
+	Xbox360RockBandDrums = "xbox360RockBandDrums"
+)
+
 // Driver represents a joystick
 type Driver struct {
 	name       string