make the i2c address of bme280 configurable (#5)

make the i2c address of bme280 configurable

The address can either be 0x76 or 0x77. It depends on hardware configuration.
If you connect SDO to GND its 0x76
If you connect SDO to V(DDIO) its 0x77.

* Add me to the authors.
* the bme280 cmd uses the new address option
* initialize default addr on definition

AUTHORS

@@ -4,4 +4,5 @@
 # some cases, their employer may be the copyright holder.  To see the full list
 # of contributors, see the revision history in source control.
 Google Inc.
+Stephan Sperber
 Thorsten von Eicken <tve@voneicken.com>

CONTRIBUTORS

@@ -27,4 +27,5 @@
 # Please keep the list sorted.
 
 Marc-Antoine Ruel <maruel@chromium.org> <maruel@gmail.com>
+Stephan Sperber <sperberstephan@googlemail.com>
 Thorsten von Eicken <tve@voneicken.com>

devices/bme280/bme280.go

@@ -117,6 +117,10 @@ func (d *Dev) Stop() error {
 // and FOff for filter if planing to call frequently, else use S500ms to get a
 // bit more than one reading per second.
 //
+// Address is only used on creation of an I²C-device. Its default value is 0x76.
+// It can be set to 0x77. Both values depend on HW configuration of the sensor's
+// SDO pin. This has no effect with NewSPI()
+//
 // BUG(maruel): Remove the Standby flag and replace with a
 // WaitForNextSample(time.Duration). Then use the closest value automatically.
 type Opts struct {
@@ -125,6 +129,7 @@ type Opts struct {
 	Humidity    Oversampling
 	Standby     Standby
 	Filter      Filter
+	Address     uint16
 }
 
 // NewI2C returns an object that communicates over I²C to BME280 environmental
@@ -133,7 +138,18 @@ type Opts struct {
 // It is recommended to call Stop() when done with the device so it stops
 // sampling.
 func NewI2C(i i2c.Conn, opts *Opts) (*Dev, error) {
-	d := &Dev{d: &i2c.Dev{Conn: i, Addr: 0x76}, isSPI: false}
+	addr := uint16(0x76)
+	if opts != nil {
+		switch opts.Address {
+		case 0x76, 0x77:
+			addr = opts.Address
+		case 0x00:
+			// do not do anything
+		default:
+			return nil, errors.New("given address not supported by device")
+		}
+	}
+	d := &Dev{d: &i2c.Dev{Conn: i, Addr: addr}, isSPI: false}
 	if err := d.makeDev(opts); err != nil {
 		return nil, err
 	}