Low-level IO driver for serial flash memory via SPI and QSPI (#124)

* QSPI/SPI: flash memory functions

examples/flash/console/spi/main.go

@@ -0,0 +1,20 @@
+package main
+
+import (
+	"machine"
+
+	"tinygo.org/x/drivers/examples/flash/console"
+	"tinygo.org/x/drivers/flash"
+)
+
+func main() {
+	console_example.RunFor(
+		flash.NewSPI(
+			&machine.SPI1,
+			machine.SPI1_MOSI_PIN,
+			machine.SPI1_MISO_PIN,
+			machine.SPI1_SCK_PIN,
+			machine.SPI1_CS_PIN,
+		),
+	)
+}