Fix a ton of golint messages.

The remainder is ALL_CAPS, underscores and golint confusion when multiple
exported variables are defined on a single line.

No functional change except one error string tweaked.

devices/bmxx80/bmx280_test.go

@@ -931,7 +931,7 @@ func BenchmarkCalibration280Float64(b *testing.B) {
 
 //
 
-var epsilon float64 = 0.000000001
+const epsilon = 0.000000001
 
 func floatEqual(a, b float64) bool {
 	return (a-b) < epsilon && (b-a) < epsilon

devices/bmxx80/bmxx80.go

@@ -125,9 +125,7 @@ const (
 	F16      Filter = 4
 )
 
-// DefaultsOpts returns the default options used.
+// DefaultOpts is the recommended default options.
-//
-// Defaults to use O4x (4x oversampling) for all measurements.
 var DefaultOpts = Opts{
 	Temperature: O4x,
 	Pressure:    O4x,

experimental/devices/cap1188/cap1188_options.go

@@ -13,6 +13,7 @@ import (
 // SamplingTime determines the time to make a single sample.
 type SamplingTime uint8
 
+// Valid SamplingTime values.
 const (
 	S320us SamplingTime = 0
 	S640us SamplingTime = 1
@@ -24,6 +25,7 @@ const (
 // AvgSampling set the number of samples per measurement that get averaged.
 type AvgSampling uint8
 
+// Valid AvgSampling values.
 const (
 	// Avg1 means that 1 sample is taken per measurement
 	Avg1   AvgSampling = iota // 0
@@ -40,7 +42,7 @@ const (
 // normal operation.
 type CycleTime uint8
 
-// Possible cycle time values. (written as 2 bits)
+// Valid CycleTime values.
 const (
 	C35ms CycleTime = iota // 0
 	C70ms                  // default
@@ -52,7 +54,7 @@ const (
 // recalibration.
 type MaxDur uint8
 
-// Possible touch duration values. (written as 4 bits)
+// Valid MaxDur values.
 const (
 	MaxDur560ms MaxDur = iota
 	MaxDur840ms