ozzo-validation Validate interface implemented for package time (#20)

* Country and currency constants moved to separate packages, module version updated to v2, several minor improvements

* added DecimalPlaces method for currency

* Updated readme

* ozzo-validation Validate interface implemented for package time

Co-authored-by: Vadim Maslov <vadim.maslov@finteqhub.com>

time/date.go

@@ -3,8 +3,10 @@ package time
 import (
 	"encoding/json"
 	"encoding/xml"
-	"gopkg.in/guregu/null.v4"
+	"fmt"
 	"time"
+
+	"gopkg.in/guregu/null.v4"
 )
 
 const format = "2006-01-02"
@@ -64,6 +66,15 @@ func (d Date) format() *string {
 	return nil
 }
 
+// Validate implementation of ozzo-validation Validate interface
+func (d Date) Validate() (err error) {
+	if !d.Valid {
+		return fmt.Errorf("'%s' is not valid date", d)
+	}
+
+	return
+}
+
 func ParseDateFromString(value string) (Date, error) {
 	if value == "" {
 		return Date{}, nil

time/time.go

@@ -4,8 +4,9 @@ import (
 	"encoding/json"
 	"encoding/xml"
 	"fmt"
-	"gopkg.in/guregu/null.v4"
 	"time"
+
+	"gopkg.in/guregu/null.v4"
 )
 
 type Time null.Time
@@ -76,6 +77,15 @@ func (t *Time) parseTimeFromString(value string) (err error) {
 	return nil
 }
 
+// Validate implementation of ozzo-validation Validate interface
+func (t Time) Validate() (err error) {
+	if !t.Valid {
+		return fmt.Errorf("'%s' is not valid time", t)
+	}
+
+	return
+}
+
 func ParseNullTimeFromString(value string) (t Time, err error) {
 	if err = t.parseTimeFromString(value); err != nil {
 		return t, err