Support for Waveshare 2.13" (B & C versions) e-paper display (#56)

* Support for Waveshare 2.13" (B) e-paper display

examples/waveshare-epd/epd2in13x/main.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"machine"
+
+	"image/color"
+
+	"github.com/tinygo-org/drivers/waveshare-epd/epd2in13x"
+)
+
+var display epd2in13x.Device
+
+func main() {
+	machine.SPI0.Configure(machine.SPIConfig{
+		Frequency: 8000000,
+		Mode:      0,
+	})
+
+	display = epd2in13x.New(machine.SPI0, machine.P6, machine.P7, machine.P8, machine.P9)
+	display.Configure(epd2in13x.Config{})
+
+	white := color.RGBA{0, 0, 0, 255}
+	colored := color.RGBA{255, 0, 0, 255}
+	black := color.RGBA{1, 1, 1, 255}
+
+	display.ClearBuffer()
+	display.ClearDisplay()
+
+	// Show a checkered board
+	for i := int16(0); i < 27; i++ {
+		showRect((i%3)*35, i*8, 35, 8, colored)
+		showRect(((i+1)%3)*35, i*8, 35, 8, black)
+		showRect(((i+2)%3)*35, i*8, 35, 8, white)
+	}
+	display.Display()
+	display.WaitUntilIdle()
+	println("You could remove power now")
+}
+
+func showRect(x int16, y int16, w int16, h int16, c color.RGBA) {
+	for i := x; i < x+w; i++ {
+		for j := y; j < y+h; j++ {
+			display.SetPixel(i, j, c)
+		}
+	}
+}