Fix typo and style (#9)

duration.go

@@ -47,7 +47,7 @@ var (
 )
 
 // Parse attempts to parse the given duration string into a *Duration,
-// if parsing fails an error is returned instead
+// if parsing fails an error is returned instead.
 func Parse(d string) (*Duration, error) {
 	if !strings.Contains(d, "P") {
 		return nil, ErrUnexpectedInput
@@ -145,7 +145,7 @@ func Parse(d string) (*Duration, error) {
 
 // FromTimeDuration converts the given time.Duration into duration.Duration.
 // Note that for *Duration's with period values of a month or year that the duration becomes a bit fuzzy
-// since obviously those things vary month to month and year to year
+// since obviously those things vary month to month and year to year.
 func FromTimeDuration(d time.Duration) *Duration {
 	duration := &Duration{}
 	if d == 0 {
@@ -186,21 +186,21 @@ func FromTimeDuration(d time.Duration) *Duration {
 	return duration
 }
 
-// Format formats the given time.Duration into an ISO 8601 duration string (e.g. P1DT6H5M),
+// Format formats the given time.Duration into an ISO 8601 duration string (e.g., P1DT6H5M),
 // negative durations are prefixed with a minus sign, for a zero duration "PT0S" is returned.
 // Note that for *Duration's with period values of a month or year that the duration becomes a bit fuzzy
-// since obviously those things vary month to month and year to year
+// since obviously those things vary month to month and year to year.
 func Format(d time.Duration) string {
 	return FromTimeDuration(d).String()
 }
 
 // ToTimeDuration converts the *Duration to the standard library's time.Duration.
 // Note that for *Duration's with period values of a month or year that the duration becomes a bit fuzzy
-// since obviously those things vary month to month and year to year
+// since obviously those things vary month to month and year to year.
 func (duration *Duration) ToTimeDuration() time.Duration {
 	var timeDuration time.Duration
 
-	// zero checks are here to avoid unnecessary math operations, on a durations such as `PT5M`
+	// zero checks are here to avoid unnecessary math operations, on a duration such as `PT5M`
 	if duration.Years != 0 {
 		timeDuration += time.Duration(math.Round(duration.Years * nsPerYear))
 	}