controller: add a lib for the HD44780 character display controller

the hd44780 package supports HD44780 character display controllers
connected by either a 4-bit GPIO bus or an I2C bus

it also includes a high-level wrapper for easily printing messages

samples/hd44780.go

@@ -0,0 +1,43 @@
+// +build ignore
+
+package main
+
+import (
+	"flag"
+	"time"
+
+	"github.com/kidoman/embd"
+	"github.com/kidoman/embd/controller/hd44780"
+
+	_ "github.com/kidoman/embd/host/all"
+)
+
+func main() {
+	flag.Parse()
+
+	if err := embd.InitI2C(); err != nil {
+		panic(err)
+	}
+	defer embd.CloseI2C()
+
+	bus := embd.NewI2CBus(1)
+
+	display, err := hd44780.NewI2CCharacterDisplay(
+		bus,
+		0x20,
+		hd44780.PCF8574PinMap,
+		20,
+		4,
+		hd44780.TwoLine,
+		hd44780.BlinkOn,
+	)
+	if err != nil {
+		panic(err)
+	}
+	defer display.Close()
+
+	display.Clear()
+	display.Message("Hello, world!\n@embd")
+	time.Sleep(10 * time.Second)
+	display.BacklightOff()
+}