Initial support for BMP180 digital pressure sensor (#11)

* Initial support for BMP180 digital pressure sensor
Note that Pressure & Temperature return int32 and millis unit (millidegrees
and mPa)

examples/bmp180/main.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"time"
+
+	"github.com/tinygo-org/drivers/bmp180"
+	"machine"
+)
+
+func main() {
+	machine.I2C0.Configure(machine.I2CConfig{})
+	sensor := bmp180.New(machine.I2C0)
+	sensor.Configure()
+
+	connected := sensor.Connected()
+	if !connected {
+		println("BMP180 not detected")
+		return
+	}
+	println("BMP180 detected")
+
+	for {
+		temp, _ := sensor.Temperature()
+		println("Temperature:", float32(temp)/1000, "ºC")
+
+		pressure, _ := sensor.Pressure()
+		println("Pressure", float32(pressure)/100000, "hPa")
+
+		time.Sleep(2 * time.Second)
+	}
+}