Benchmark related changes

- .gohci.yml: Run with both -cover and -bench on odroid and win10 and make the
  benchtime 1000ms instead of 10ms to increase precision, as this was lacking.
- apa102: add benchmark for toRGBFast()
- bmxx80: add benchmark for conversion functions.
- gpiotest: silence test (was leaking output during benchmarks)
- physic: add benchmark for the current int64 String() implementation compared
  to an hypothetical (simpler) float64 based implementation.

devices/apa102/temperature_test.go

@@ -15,3 +15,11 @@ func TestToRGBFast_limits(t *testing.T) {
 		t.Fatal(r, g, b)
 	}
 }
+
+func BenchmarkToRGBFast(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		if r, g, blue := toRGBFast(30000); r != 159 || g != 191 || blue != 255 {
+			b.FailNow()
+		}
+	}
+}

devices/bmxx80/bmx280_test.go

@@ -805,6 +805,48 @@ func TestCalibration280_compensateHumidityInt(t *testing.T) {
 	}
 }
 
+func BenchmarkCalibration280Int32(b *testing.B) {
+	tRaw := int32(524112)
+	pRaw := int32(309104)
+	hRaw := int32(30987)
+	for i := 0; i < b.N; i++ {
+		temp, tFine := calib280.compensateTempInt(tRaw)
+		pres := calib280.compensatePressureInt32(pRaw, tFine)
+		humi := calib280.compensateHumidityInt(hRaw, tFine)
+		if tFine != 117407 || temp != 2293 || pres != 100045 || humi != 64686 {
+			b.FailNow()
+		}
+	}
+}
+
+func BenchmarkCalibration280Int64(b *testing.B) {
+	tRaw := int32(524112)
+	pRaw := int32(309104)
+	hRaw := int32(30987)
+	for i := 0; i < b.N; i++ {
+		temp, tFine := calib280.compensateTempInt(tRaw)
+		pres := calib280.compensatePressureInt64(pRaw, tFine)
+		humi := calib280.compensateHumidityInt(hRaw, tFine)
+		if tFine != 117407 || temp != 2293 || pres != 25611063 || humi != 64686 {
+			b.FailNow()
+		}
+	}
+}
+
+func BenchmarkCalibration280Float64(b *testing.B) {
+	tRaw := int32(524112)
+	pRaw := int32(309104)
+	hRaw := int32(30987)
+	for i := 0; i < b.N; i++ {
+		temp, tFine := calib280.compensateTempFloat(tRaw)
+		pres := calib280.compensatePressureFloat(pRaw, tFine)
+		humi := calib280.compensateHumidityFloat(hRaw, tFine)
+		if tFine != 117494 || !floatEqual(temp, 22.948120) || !floatEqual(pres, 100.046074) || !floatEqual(humi, 63.167889) {
+			b.FailNow()
+		}
+	}
+}
+
 //
 
 var epsilon float32 = 0.00000001