image: add support for image/jpeg and image/png (#303)

* Copy from go1.17 image package
* Remove unnecessary files
* Reduce memory usage
* Add examples/ili9341/slideshow
* image: add ./image/README.md
* image: change convert2bin to . /cmd
* Makefile: add ./cmd to NOTEST

examples/ili9341/slideshow/atsamd21.go

@@ -0,0 +1,29 @@
+// +build atsamd21
+
+package main
+
+import (
+	"machine"
+
+	"tinygo.org/x/drivers/ili9341"
+)
+
+var (
+	display = ili9341.NewSPI(
+		machine.SPI0,
+		machine.D0,
+		machine.D1,
+		machine.D2,
+	)
+
+	backlight = machine.D3
+)
+
+func init() {
+	machine.SPI0.Configure(machine.SPIConfig{
+		SCK:       machine.SPI0_SCK_PIN,
+		SDO:       machine.SPI0_SDO_PIN,
+		SDI:       machine.SPI0_SDI_PIN,
+		Frequency: 24000000,
+	})
+}