shifter: simplify API surface for PyBadge (#137)

* shifter: simplify API surface and use build directive to directly match the PyBadge

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

* shifter: further simplify API for PyBadge

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

examples/shifter/main.go

@@ -1,53 +1,42 @@
+// This example is designed to implement the button shifter for a PyBadge.
 package main
 
 import (
-	"machine"
 	"time"
 
 	"tinygo.org/x/drivers/shifter"
 )
 
-const (
-	BUTTON_LEFT = iota
-	BUTTON_UP
-	BUTTON_DOWN
-	BUTTON_RIGHT
-	BUTTON_SELECT
-	BUTTON_START
-	BUTTON_A
-	BUTTON_B
-)
-
 func main() {
-	buttons := shifter.New(shifter.EIGHT_BITS, machine.BUTTON_LATCH, machine.BUTTON_CLK, machine.BUTTON_OUT)
+	buttons := shifter.NewButtons()
 	buttons.Configure()
 
 	for {
 		// Update the pins state, to later be returned by .Get()
-		buttons.Read8Input()
+		buttons.ReadInput()
 
-		if buttons.Pins[BUTTON_LEFT].Get() {
+		if buttons.Pins[shifter.BUTTON_LEFT].Get() {
 			println("Button LEFT pressed")
 		}
-		if buttons.Pins[BUTTON_UP].Get() {
+		if buttons.Pins[shifter.BUTTON_UP].Get() {
 			println("Button UP pressed")
 		}
-		if buttons.Pins[BUTTON_DOWN].Get() {
+		if buttons.Pins[shifter.BUTTON_DOWN].Get() {
 			println("Button DOWN pressed")
 		}
-		if buttons.Pins[BUTTON_RIGHT].Get() {
+		if buttons.Pins[shifter.BUTTON_RIGHT].Get() {
 			println("Button RIGHT pressed")
 		}
-		if buttons.Pins[BUTTON_SELECT].Get() {
+		if buttons.Pins[shifter.BUTTON_SELECT].Get() {
 			println("Button SELECT pressed")
 		}
-		if buttons.Pins[BUTTON_START].Get() {
+		if buttons.Pins[shifter.BUTTON_START].Get() {
 			println("Button START pressed")
 		}
-		if buttons.Pins[BUTTON_A].Get() {
+		if buttons.Pins[shifter.BUTTON_A].Get() {
 			println("Button A pressed")
 		}
-		if buttons.Pins[BUTTON_B].Get() {
+		if buttons.Pins[shifter.BUTTON_B].Get() {
 			println("Button B pressed")
 		}
 		time.Sleep(100 * time.Millisecond)