Shiftregister implementation (#135)

* Basic support of SIPO shift register

* typo

* add example of shiftregister for arduino and nucleo

* Fix build flag for nucleof103rb

* Fix wrong data pin configuration

* Change README.md for Shift registers

* Add API for individual register's output pin

* Rewrite shift register example to show ShiftPin usage

* Fix target for shiftregister example smoke test

* Fix type in makefile

* Add shiftregister compatble IC

* Edit comment and readme

examples/shiftregister/main.go

@@ -0,0 +1,124 @@
+package main
+
+import (
+	"machine"
+	"time"
+
+	"tinygo.org/x/drivers/shiftregister"
+)
+
+func main() {
+	d := shiftregister.New(
+		shiftregister.EIGHT_BITS,
+		machine.PA6, // D12 Pin latch connected to ST_CP of 74HC595 (12)
+		machine.PA7, // D11 Pin clock connected to SH_CP of 74HC595 (11)
+		machine.PB6, // D10 Pin data connected to DS of 74HC595 (14)
+	)
+	d.Configure()
+
+	for {
+
+		// Examples using masks. This method writes all pins state at once.
+
+		// All pins High
+		d.WriteMask(0xFF)
+		delay()
+
+		// All pins Low
+		d.WriteMask(0x00)
+		delay()
+
+		// Some fun with masks
+		for _, pattern := range patterns {
+			d.WriteMask(pattern)
+			shortDelay()
+		}
+		delay()
+		d.WriteMask(0x00)
+
+		// Examples using individually addressable pin API. This method is slower than using mask
+		// because all register's pins state are send for is p.Set() call.
+
+		// Set register's pin #4
+		d.GetShiftPin(4).High()
+		delay()
+		d.GetShiftPin(4).Low()
+		delay()
+
+		// Get an individual pin and use it
+		pin := d.GetShiftPin(7)
+		pin.High()
+		delay()
+		pin.Low()
+		delay()
+
+		// Prepare an array of pin attached to the register
+		pins := [8]*shiftregister.ShiftPin{}
+		for p := 0; p < 8; p++ {
+			pins[p] = d.GetShiftPin(p)
+		}
+
+		for p := 7; p >= 0; p-- {
+			pins[p].Low()
+			shortDelay()
+			pins[p].High()
+		}
+
+		for p := 7; p >= 0; p-- {
+			pins[p].High()
+			time.Sleep(100 * time.Millisecond)
+			pins[p].Low()
+		}
+		delay()
+	}
+}
+
+func delay() {
+	time.Sleep(500 * time.Millisecond)
+}
+func shortDelay() {
+	time.Sleep(100 * time.Millisecond)
+}
+
+var patterns = []uint32{
+	0b00000001,
+	0b00000010,
+	0b00000100,
+	0b00001000,
+	0b00010000,
+	0b00100000,
+	0b01000000,
+	0b10000000,
+	0b10000001,
+	0b10000010,
+	0b10000100,
+	0b10001000,
+	0b10010000,
+	0b10100000,
+	0b11000000,
+	0b11000001,
+	0b11000010,
+	0b11000100,
+	0b11001000,
+	0b11010000,
+	0b11100000,
+	0b11100001,
+	0b11100010,
+	0b11100100,
+	0b11101000,
+	0b11110000,
+	0b11110001,
+	0b11110010,
+	0b11110100,
+	0b11111000,
+	0b11111001,
+	0b11111010,
+	0b11111100,
+	0b11111101,
+	0b11111110,
+	0b11111111,
+	0b00000000,
+	0b11111111,
+	0b00000000,
+	0b11111111,
+}