fix examples_test output and various opts comments

Author: vesari

prometheus/desc.go

@@ -47,7 +47,7 @@ type Desc struct {
 	fqName string
 	// help provides some helpful information about this metric.
 	help string
-	// unit provides the unit of this metric
+	// unit provides the unit of this metric.
 	unit string
 	// constLabelPairs contains precalculated DTO label pairs based on
 	// the constant labels.

prometheus/examples_test.go

@@ -308,9 +308,9 @@ func ExampleRegister() {
 
 	// Output:
 	// taskCounter registered.
-	// taskCounterVec not registered: a previously registered descriptor with the same fully-qualified name as Desc{fqName: "worker_pool_completed_tasks_total", help: "Total number of tasks completed.", constLabels: {}, variableLabels: {worker_id}} has different label names or a different help string
+	// taskCounterVec not registered: a previously registered descriptor with the same fully-qualified name as Desc{fqName: "worker_pool_completed_tasks_total", help: "Total number of tasks completed.", unit: "", constLabels: {}, variableLabels: {worker_id}} has different label names or a different help string
 	// taskCounter unregistered.
-	// taskCounterVec not registered: a previously registered descriptor with the same fully-qualified name as Desc{fqName: "worker_pool_completed_tasks_total", help: "Total number of tasks completed.", constLabels: {}, variableLabels: {worker_id}} has different label names or a different help string
+	// taskCounterVec not registered: a previously registered descriptor with the same fully-qualified name as Desc{fqName: "worker_pool_completed_tasks_total", help: "Total number of tasks completed.", unit: "", constLabels: {}, variableLabels: {worker_id}} has different label names or a different help string
 	// taskCounterVec registered.
 	// Worker initialization failed: inconsistent label cardinality: expected 1 label values but got 2 in []string{"42", "spurious arg"}
 	// notMyCounter is nil.

prometheus/histogram.go

@@ -372,7 +372,7 @@ type HistogramOpts struct {
 	// string.
 	Help string
 
-	//Unit provides the unit of this Histogram
+	//Unit provides the unit of this Histogram.
 	Unit string
 
 	// ConstLabels are used to attach fixed labels to this metric. Metrics

prometheus/metric.go

@@ -81,7 +81,7 @@ type Opts struct {
 	// string.
 	Help string
 
-	// Unit provides the unit of this metric
+	// Unit provides the unit of this metric.
 	Unit string
 
 	// ConstLabels are used to attach fixed labels to this metric. Metrics

prometheus/summary.go

@@ -101,7 +101,7 @@ type SummaryOpts struct {
 	// string.
 	Help string
 
-	// Unit provides the unit of the metric
+	// Unit provides the unit of this Summary.
 	Unit string
 
 	// ConstLabels are used to attach fixed labels to this metric. Metrics