Split registries into their own packages. (#122)

conn/gpio -> conn/gpio/gpioreg
conn/i2c -> conn/i2c/i2creg
conn/spi -> conn/spi/spireg
conn/pins -> conn/pin
host/headers -> conn/pin/pinreg
conn/reg -> conn/mmr

devices/apa102/apa102_test.go

@@ -15,6 +15,7 @@ import (
 	"testing"
 
 	"periph.io/x/periph/conn/spi"
+	"periph.io/x/periph/conn/spi/spireg"
 	"periph.io/x/periph/conn/spi/spitest"
 )
 
@@ -558,7 +559,7 @@ func TestInit(t *testing.T) {
 //
 
 func Example() {
-	bus, err := spi.Open("")
+	bus, err := spireg.Open("")
 	if err != nil {
 		log.Fatalf("failed to open SPI: %v", err)
 	}

devices/bme280/bme280_test.go

@@ -9,7 +9,7 @@ import (
 	"log"
 	"testing"
 
-	"periph.io/x/periph/conn/i2c"
+	"periph.io/x/periph/conn/i2c/i2creg"
 	"periph.io/x/periph/conn/i2c/i2ctest"
 	"periph.io/x/periph/devices"
 )
@@ -140,7 +140,7 @@ func TestCalibrationInt(t *testing.T) {
 //
 
 func Example() {
-	bus, err := i2c.Open("")
+	bus, err := i2creg.Open("")
 	if err != nil {
 		log.Fatalf("failed to open I²C: %v", err)
 	}

devices/ds248x/ds248x_test.go

@@ -8,7 +8,7 @@ import (
 	"fmt"
 	"testing"
 
-	"periph.io/x/periph/conn/i2c"
+	"periph.io/x/periph/conn/i2c/i2creg"
 	"periph.io/x/periph/conn/i2c/i2ctest"
 )
 
@@ -32,7 +32,7 @@ func TestInit(t *testing.T) {
 
 func Example() {
 	// Open the I²C bus to which the DS248x is connected.
-	i2cBus, err := i2c.Open("")
+	i2cBus, err := i2creg.Open("")
 	if err != nil {
 		fmt.Println(err)
 		return
@@ -72,7 +72,7 @@ func TestRecordInit(t *testing.T) {
 	}
 	host.Init()
 
-	i2cReal, err := i2c.Open("")
+	i2cReal, err := i2creg.Open("")
 	if err != nil {
 		t.Fatal(err)
 	}

devices/lirc/lirc.go

@@ -14,7 +14,7 @@ import (
 	"strings"
 	"sync"
 
-	"periph.io/x/periph/conn/gpio"
+	"periph.io/x/periph/conn/gpio/gpioreg"
 	"periph.io/x/periph/conn/ir"
 )
 
@@ -220,12 +220,12 @@ func (d *driver) Init() (bool, error) {
 		return false, nil
 	}
 	if in != -1 {
-		if err := gpio.RegisterAlias("IR_IN", in); err != nil {
+		if err := gpioreg.RegisterAlias("IR_IN", in); err != nil {
 			return true, err
 		}
 	}
 	if out != -1 {
-		if err := gpio.RegisterAlias("IR_OUT", out); err != nil {
+		if err := gpioreg.RegisterAlias("IR_OUT", out); err != nil {
 			return true, err
 		}
 	}

devices/ssd1306/ssd1306_test.go

@@ -14,7 +14,7 @@ import (
 	"golang.org/x/image/font/basicfont"
 	"golang.org/x/image/math/fixed"
 
-	"periph.io/x/periph/conn/i2c"
+	"periph.io/x/periph/conn/i2c/i2creg"
 	"periph.io/x/periph/conn/i2c/i2ctest"
 	"periph.io/x/periph/devices/ssd1306/image1bit"
 )
@@ -77,7 +77,7 @@ func TestDraw1D(t *testing.T) {
 //
 
 func Example() {
-	bus, err := i2c.Open("")
+	bus, err := i2creg.Open("")
 	if err != nil {
 		log.Fatalf("failed to open I²C: %v", err)
 	}

devices/tm1637/tm1637_test.go

@@ -8,7 +8,7 @@ import (
 	"log"
 	"testing"
 
-	"periph.io/x/periph/conn/gpio"
+	"periph.io/x/periph/conn/gpio/gpioreg"
 	"periph.io/x/periph/conn/gpio/gpiotest"
 	"periph.io/x/periph/host"
 )
@@ -30,7 +30,7 @@ func Example() {
 	if _, err := host.Init(); err != nil {
 		log.Fatalf("failed to initialize periph: %v", err)
 	}
-	dev, err := New(gpio.ByNumber(6), gpio.ByNumber(12))
+	dev, err := New(gpioreg.ByNumber(6), gpioreg.ByNumber(12))
 	if err != nil {
 		log.Fatalf("failed to initialize tm1637: %v", err)
 	}