all: introduce a temperature type

This type should be used whenever a sensor (or actuator?) works with a
temperature. For example, this commit changes the signature:

    ReadTemperature() (int32, error)

to the following:

    ReadTemperature() (drivers.Temperature, error)

I believe this is much clearer in intent. It also makes it trivial to
introduce common conversions. For example, there are already Celsius()
and Fahrenheit() methods to convert to the given units, as a floating
point. More units could be added as needed, for example a CelsiusInt().

dht/constants.go

@@ -35,18 +35,6 @@ func (d DeviceType) extractData(buf []byte) (temp int16, hum uint16) {
 	return
 }
 
-// Celsius and Fahrenheit temperature scales
-type TemperatureScale uint8
-
-func (t TemperatureScale) convertToFloat(temp int16) float32 {
-	if t == C {
-		return float32(temp) / 10
-	} else {
-		// Fahrenheit
-		return float32(temp)*(9.0/50.) + 32.
-	}
-}
-
 // All functions return ErrorCode instance as error. This class can be used for more efficient error processing
 type ErrorCode uint8
 
@@ -57,9 +45,6 @@ const (
 	DHT11 DeviceType = iota
 	DHT22
 
-	C TemperatureScale = iota
-	F
-
 	ChecksumError ErrorCode = iota
 	NoSignalError
 	NoDataError